Setting up a sanctuary is not only common, it is a smart deer management practice. Deer tend to go where they feel safe. You would rather that "safe zone" be on your property. A Sanctuary is as important as your treestand. The deer may not know the exact boundries of the sanctuary, but they will find the area where they aren't being pressured quickly enough.

As for the problem at hand, I would let you friend have the antler. They are not worth fighting over. It isn't like he found a 200 inch plus deer. Let him have them and you might be able to keep the friendship.

I also wouldn't invite him to join the lease or invite him to hunt again. He obviously doesn't respect any of your rules and it will be 10 times worse if he is a member.