I've got a couple dozen pines coming up. The deer love them when they are small, apparently the needles are delicious; and when they get about 4 to 5 feet tall, the young bucks have a great time rubbing them to death.
I use plain old sulfur powder, the pure stuff sold to kill aphids. Just sprinkle some on the needles within browsing reach and the trunk when it gets big enough. Rotten eggs work better, but mixing with water and spraying is not fun.
Also, since I have plenty of black locust and multi-flora rose bushes, I find thorny lengths and arrange them around the saplings so the deer's nose will have to be used to get at anything on the tree and that works. But does need regular attention.
Long term I'm working on a deer barrier about 20 feet wide that will have stuff they like to eat on their side, some stuff they don't like to push through (woodland sunflowers have stalks I don't like to brush with my skin and apparently deer don't either) in the middle and stuff I want to eat on my side, the garden side.