Deer can be the bane of any gardener, especially one which happens to be growing tasty apple trees. Note that a method that works for one deer, may not work for another. So, you'll need to rely on trial and error or using multiple methods at the same time. You will also need to change methods after a while, to maintain their effectiveness. The worst deer damage occurs in the late fall through the early spring.
Get a dog and install an invisible fence--for the dog, not the deer. Dogs on chains or in pens will not be effective, nor will dogs that are inside most of the day or night.
Build a fence. Fences must be at least 5 feet tall if they are solid and 8 feet tall if they are not solid. Black plastic mesh, while not attractive, is effective and will last for several years.
Circle young trees with 6-foot-high chicken wire.
Use an electric fence. You can use electric fences alone or on top of shorter fences.
Drape the trees with flashing holiday lights. Deer will stay away from the shadows cast by the lights, but only temporarily.
Use gas exploders or strobe light sirens. These detonate at regular intervals and will scare the deer. Unfortunately, they are only effective for a couple of weeks and are expensive. These may also drive away your neighbors, but tend to attract the police and complaints.
Motion detector sprinklers, often known as "scarecrows," are good at repelling deer. These will blast anything that moves, which includes children and dogs.
Purchase and use commercial deer repellents. Repellents may be contact repellents, which makes the trees taste bad, or odor repellents, which makes an area smell bad.
Place human hair, either your own or obtain some from a salon, into a nylon stocking. Hang the stockings on the tree. For best results, use dirty hair and not hair recently shampooed.
Mix 5 tbsp. cayenne pepper or 2 tbsp. hot pepper or Tabasco sauce with 1 gallon of water. Add 1 tbsp. vegetable oil. Mix well and spray onto the apple tree.
Blend two eggs and 1 cup cold water at high speed. Add mixture to 1 gallon of water. Let stand for 24 hours. Spray the mixture on foliage near the apple tree. Reapply two to three times a year.
Place three red cayenne, jalapeno or habanera fresh peppers into a food processor with enough water so it creates a liquid when processed. Strain the liquid through a cheesecloth into a glass quart jar. Add 2 tbsp. of olive or vegetable oil. Add a squirt of white glue and a two drops of liquid dish-washing detergent. Use 1 part of mixture with 10 parts water. Shake well. Apply the mixture to the apple trees. Reapply after rain.
Place a couple of bars of Dial or Irish Spring soap in a nylon stocking. Hang several around the trees. Some say that perfumed or deodorant soaps work better than non-deodorant soaps.
Use fertilizers such as Repellex or Milorganite. Both have been said to be effective deer repellents.
Spray predator urine or manure around the trees. You can buy these at many garden stores, although some say human urine is just as effective (and less expensive).