I've tried all the remedies everyone else has used, from predator scents (what predators? They don't know what one is supposed to smell like because there haven't been any in our part of the world for decades) to vile rotten egg sprays, to plastic tubes that looked like this and made me feel as though we lived in a natural gas pipe field:
Wrapping each and every tree and shrub is impossible and unsightly. Perimeter fences, either electric or 12 foot high barriers, are equally out of the question. Motion-triggered water sprays aren't practical in the winter here, and would litter the landscape with hoses everywhere. I really needed another way.
The solution: Wireless deer zappers that deliver a mild electric shock on contact. They are one foot high plastic stakes that hold two AA batteries, which last for a year. At the top of the stake is a clear plastic saturated scent lure. The deer smells it, wanders over, licks it, and gets a surprise. It's not harmful... I've touched it myself and it made me jump and say a bad word, but it doesn't hurt. Although I didn't actually put my tongue on it.
You may not want to use these if children or pets play in your yard.
You don't protect plants with these, instead you modify the routes the deer take amidst all your plantings. I think they are working. In past winters my China Girl hollies (ilex meserveae) always got pruned by the hungry deer into such raggy shapes. For 3 years, this is what I had every spring:
This week I gathered up all the stakes to replace the batteries and put them back out in slightly different locations for novelty and surprise. I found 11 of the 12 stakes. The last one? Gone to where the lonely socks from the dryer go? Taken by the deer for study and examination to figure out how they work? Lying on its side in the mud right in front of me where I'm likely to step on it and get my toes zapped? Where could it be?
I don't know if the deer will figure out it's only the green stakes that shock them, and learn to eat around the zappers. For now the deer seem to be wary of their normal route through my yard, and the stakes are pretty inconspicuous in the landscape, especially as plants grow and fill in.
Wireless technology to combat deer: it's just so 21st century. I call them iZaps... I'm sure you'll be able to get them soon from iTunes.