Deer will eat garden plants, sometimes all of them! They also can damage trees and shrubs by rubbing against them and chewing on branches.
Prevent problems before they appear
Fence them out. The most effective deer control is a tall fence, at least 7 feet high, around the garden or yard. Individual plants can be protected using strong wire-mesh cylinders at least 5 feet high.
Use plants deer don’t like to eat. Reduce damage to the garden by using deer-resistant plants for ornamental plantings. The Sunset Western Garden Book has useful lists. Also ask your local nursery. Deer plant preferences may vary by area and over time, so be prepared to experiment.
Switch products frequently if using repellents and noisemakers. There are many products sold to repel or frighten deer, but they can become ineffective once the deer get used to them. Switch to something else fairly often, and reapply after rains.