I find that the white plastic protective wraps around young trees reduces deer rub frequency.

If a deer has detected that you paid enough money for a tree, you could plant it on your roof and they would set up a ladder climb to the roof to destroy it. There would be nothing left but a nub in the morning.

I've lost so many trees to deer over the years trying to get a small orchard started. I am finally getting someplace, but it took fences around everything until they were too large to eat in one night. There is no rule of thumb against rubs, apart from leaving a lot of low, stiff branches on the trees that the deer's antlers get hung up on. They prefer those nice, straight poles that hit 5-6 feet before the first branch. Pine trees do not have those stiff branches, they just disintegrate under the onslaught.