This is a two part response.

First, if you friend does not respect the fact that this has been your honey hole for years, then he is not a good friend. If the two of you found it and scouted it together that is one thing but if it was yours exclusively and he is now moving in, that is just a lack of respect or character as Arthur suggested.

Secondly, you said it's on public land so your right, you have no rights to it. Even if your friend does not hunt it, you have no idea who is. Someone else may think they are guarding it for themselves and being careful not to leave sign that you will see. A friend of mine said something when we found a nice spot on Federal land. "You can bet that if we found it, twenty other people know about it also." I was hunting it on Friday and another hunter walked within 60 yards of me before he saw me waving my arms.

I wouldn't scout it while they were hunting there just to screw up their chances. That will only escalate an already bad situation. Who knows what kind of retribution they will come up with. Just chalk it up to a learning experience on who your true friends are.