"Deer Proofing your Yard and Garden" is a book by Rhonda Massingham Hart that came out in 1997 and is chocked full of relevant research on understanding deer and their habits.

I agree with her conclusion that deer are very adaptable, and an effective deterrent system should use multiple methods of making the deer feel unsafe. That's the main reason why my current deterrent design uses motion in conjunction with sound.

The picture above shows how to set up a simple electric fence barrier with a shocking peanut butter surprise. I think this would be a good backup to a mechanical deterrent for folks who don't have a dog, but our Lucy would most likely find it first and we want her to continue to patrol the perimeter.

Techlib.com has an intriguing circuit that might be of interest to some back yard deer deterrent experimenters out there.

It detects seismic vibrations from a person or large animal and then sets off a wireless doorbell buzzer for a few seconds to startle whover is nearby.

They label it as a deer repellant for the garden, but I would be concerned about the protective range this thing has. It might work for a garden with low level deer traffic and maybe just one entrance, but our large perimeter here would require dozens of these to cover the whole area. There's no data presented about testing on a real garden, so I would think twice about this approach before investing too much time in it. In fact I feel pretty confident you would get better results with my current design no matter what situation you have, but that's just me.

I learned from reading Jim Arnosky's excellent juvenile book "All About Deer" a key element that must be fully understood by the back yard deer deterrent maker.

"A deer can swivel each of its ears around on its head to listen in two different directions at once."

This fact indicates that even the smallest garden could benefit by deploying at least two deterrents at each end of the protected area.

In my opinion the sound puts a deer in caution mode, but it's the movement that usually provokes bolting.

This is what your basic DC motor gearbox looks like. The gear configuration helps to slow it down and provide more torque than just the motor spinning by itself.

I ordered this one from a robotic supplier named Pololu. The cost was around 12 bucks once shipping is factored in.

The instructions that came with the kit are a challenge to understand. Luckily they have great illustrations to guide you in the right direction.

You can arrange the gears in a way that gives you 4 choices of speed.
                                                                                                
Consider this an advanced project. Those gears are small and you really need to get it just right for a smooth operation. It took me about 2 hours of messing with it to finally get some decent results. If you do order this kit you might want to add on one of their DC transformers for only 5 bucks.

If you've got an old computer laying around it might be possible to use it as a dedicated multi timer control center.

Timer 5.0.0 provides the ultimate control of up to 24 channels via 3 printer ports. The program enables your home computer to control relays, solenoids, pumps, or whatever you can imagine.

It's too complex of a solution for my tastes, but some of you out there might start with a timer for your deer deterrent and find out how much fun it might be to control your sprinklers and security lights once you've got the system in place.

I could see this also controlling an automatic chicken coop door by customizing each day's close time to account for the changing bed times through the year.

I've been reading African-American Gardens and Yards in the Rural South --- more on the gardening aspects of the book next week on our homestead blog --- and was intrigued to find a section on deer deterring.  The author, Richard Westmacott, interviewed 47 gardeners in Alabama, Georgia, and South Carolina, and discovered that deer were a big problem in most of their gardens.  The usual scare tactics were tried, most of which didn't work.  But the gardener who invented this unique method said that it did work:

We've tried peeing around the garden with little luck, but I can see how Sadie's method makes the smell go much further.  If you live out in the country and are desperate, this method might be worth a shot!

Grandpa Brock built a deer deterrent that works on exactly the same principle as ours --- many thanks to his grandson for pointing me in the direction of the embedded youtube video.  If you watch through to the end, you'll notice that Grandpa Brock adds a pebble to the can to mix up the sound a bit.  We're coming to realize that minor adjustments like this are enough to keep the deer on their toes and out of the garden.

Transport Canada didn't focus on deer deterrents as a way to keep deer out of airports.  Instead, they concluded "In most cases, the use of deer deterrent techniques should be used only to provide temporary control until a more permanent solution, such as fencing, removal or killing, can be found."  So far (knock on wood), we've found our deterrents to be a permanent solution.  But we're just now reaching the end of our first twelve months.  So, in case Mark's clangers fail, here are Transport Canada's top recommendations for more permanent control:

• Habitat modification can be used to reduce an area's attractiveness to deer.  "Typical actions include the pruning or removal of trees and shrubs; and the removal of standing water (ponds, ditches, puddles), alteration of grass heights, selection of broad-leaved herbaceous plants (forbs) for planting, and paving. The main goal is to reduce the airport property's attractiveness to wildlife."  This is probably a good idea at an airport, but clearly isn't going to cut it here on the homestead where we're actively working to encourage most wildlife.
  
• Fencing is Transport Canada's primary recommendation for a permanent solution.  They recommend that deer fences be 10 feet tall and consist of galvanized steel chain-link or high-tensile fixed-knot.  On the other hand, they note that electric fences "are effective in excluding deer under favourable conditions, but they will be penetrated when deer are motivated to cross them, when short-circuited by tall plant growth, or if snow accumulations exceed the height of the lower electric lines."  I don't doubt that a ten foot tall chain-link fence would keep the deer out, although I do doubt that I could ever afford to fence in our two acre garden and orchard to this level.
  

The entire article is interesting reading, and I recommend you start from the beginning and browse the whole thing.  Thanks again for sharing, Dave!

Dave left a comment a couple of weeks ago linking to Transport Canada's Deer Exclusion Devices and Deterrent Techniques.  While we were researching our own deterrent, I read a similar document put out by a U.S. state (can't remember which one) noting the best way to keep deer off airport runways.  It sounds like airports are working hard to find a way to deter deer!

I've excerpted a few of Transport Canada's key findings about deer deterrents since they match our experience:

"The key to success when using frightening methods and repellents is to use them at the first sign of a deer problem."  This has been our experience as well.  Once deer find that tasty strawberry plant, it's going to take a lot more than a gentle clanging to chase them away.  But if you deter the deer before they find your garden's tasty crops, they will keep out.

"The general obstacle to the use of sound for effective animal control is habituation.  Many animals adapt to new sounds and learn to ignore them if they are not associated with real danger....  Shooting has been used to frighten or kill deer in agricultural fields.... In these situations, deer are often killed to reinforce the effectiveness of non-lethal deer scaring devices."  I have to admit that I back up our deer deterrents with a bit of hunting, and I think it helps.

"Gas cannons can be more effective at dispersing deer if the frequency of the explosions is varied and if the cannons are moved every second or third day of use to a different area....  Motion-activated exploders, triggered by passing deer were more effective than exploders that fired at regular intervals.  Thus, the exploders only fired when a deer was close by, which made habituation less likely."  We're not using cannons (boy was someone desperate!), but Mark is working on making our deer deterrents less regular to get the same effect.

Transport Canada notes that ultrasonic noise, reflecting surfaces, and blinking lights don't work.  That's been our experience as well.  They note that odor and taste-based repellents "are only even partially effective at protecting very small areas."

Stay tuned for more gems from Transport Canada later in the week!

We're always looking for innovative ways to keep deer out of the garden, so I thought I'd share this example from the blogosphere.  Freshman Farmer writes:

That does sound like quite a simple solution, although I'm sticking to Mark's deer deterrent since it is proven in our high deer pressure area.  If anyone else has tried out fishing line, though, I'd like to hear about your results!