In many areas, deer will also browse young chestnut tops just like they will apples. I saw a volunteer Chinese Chestnut seedling the other day at my place, and the top of it had been eaten severely. What I've learned about the height of cages is that a 4 foot high cage will protect from rubbing but not from having the tops eaten. For that reason, I always use 5 foot high cages on any small tree but will still use a 4 foot high cage if I'm protecting something tall enough that they can't reach the top. Diameter of the cage is a personal choice, but there obviously comes a point when you can get the diameter too small or too big. As I have experimented with different cage diameters over the years, I now lean toward bigger being better. I makes it easier for me to open the cage up and do maintenance down the road, such as killing blackberry briers that come up at the base of the tree.