I lost up to 100 of my trees the first year to deer eating the tops off my trees. It's very frustrating losing trees to animals after you put so much time and money into making them grow. I used a lot of things to keep deer out of my trees but the best solution I found is rotten eggs. Just take 12-18 eggs and scramble them in a 1 gallon bucket and cover it and put it in the sun so it spoils quickly. Add water to fill the one gallon bucket after the eggs really start to smell which is around 5-7 days. Take a turkey baster and drip the egg mixture down the top of the tree and/or branches. The egg mixture will dry fast. In about 3 days, you will not smell it unless you get just a few inches away from the trees. Deer will avoid trees that smell bad since taste and smell go together. This egg mixture is cheap under $2 per treatment and it also contains nitrogen which fertilizes trees when it washes off. I apply this egg mixture as soon as possible to the trees tops. If the tops of the trees are not eaten, the tree grows faster. Apply the mixture every spring and again later in the summer and fall for the first 2-3 years or until the tree tops are taller than the deer.
Anything that smells and looks human will keep deer out of your trees. I use solar lights, large garbage cans with human scented items in them on sticks and move them around the yard. The light, objects moving around the yard, and smells will keep deer wandering and/or are afraid hunters are close by. It does work as long as you keep moving items around, and keep the scent strong. The strongest human scent is sweat and feces. You can use your own imagination on how to get this on rags that you can post around the trees. Human hair scattered around the trees has also been used to keep wildlife out of the trees. I even go out in the trees at night or evenings so the deer see you out there. This keeps does and small fawns out of the trees. All these options are very cheap and will work especially if your neighbors have trees. If their trees smell better, deer will stay in their shelterbelts and stay away from your trees.