Scent-based repellents use various odors to repel the deer before they take a bite.  This category includes lots of store bought products as well as homemade repellents like human pee, human hair, and scented soaps.  The goal is to make deer think that a predator is hanging out in the garden, waiting to leap on them.

So, do these repellents work?  Repellents with a sulfur smell --- like rotten eggs or blood-meal --- are the most effective, but I wouldn't want to trust my strawberries to them.  The problem with repellents (and the reason stores love to sell them) is that you have to keep reapplying them for the repellents to be effective.  Many will wash away after the first thunderstorm.  Other products bind the smell to an oil or wax which is supposed to make the product effective for several months, but you have to be sure to keep spraying every week anyway to protect your plants' new growth. 

I have tried a lot of these repellents (especially the homemade ones), and I have to say that none of them have worked for me.