If you suspect that a deer or rabbit is eating your plants, a close look at the damaged plant often reveals the culprit. Look where the plant was bitten. Is the damaged edge clean-cut or ragged?
A neatly clipped plant is a tell-tale sign of rabbit feeding. Often, the cut is angled at 45 degrees.
Rough or ragged damage was most likely caused by deer. Deer don't have upper incisors (teeth in the front that snip) so they pull and rip their food.
If leaf damage consists of small holes or chewed areas, you likely have slug or insect damage. The University Minnesota Extension webpage What's Wrong with My Plant? can help you diagnose the problem and suggest treatments.
How Can I Reduce Damage to My Plants from Deer & Rabbits?
Remove items such as bird feeders and fallen fruit (i.e. apples) that attract deer. If you don't want to remove your bird feeder, raise it so that it's at least 5 feet off the ground.
Use a commercial deterrent product. Read and follow instructions – you may need to re-apply after rain or on new plant growth. Also, alternate different products so that wildlife don't get used to any particular taste or smell.
Build a fence to protect vulnerable plants. Consider fence durability, height, and size of openings.
Protect individual shrubs and trees with a tree guard or cylinder of galvanized mesh (i.e. hardware cloth).
Try mechanical deterrents such as motion-activated lights or sprinklers.
Select deer or rabbit-resistant plants. Keep in mind that wildlife are more selective when there's an abundance of plant foods in the neighborhood but may eat "resistant" plants when food options are limited: