You sound reasonable. Find them when they are not in the tree stand and have a conversation. I always advise non-hunting, landowners to allow at least one person to hunt. If they do, you have one hunter. If they don't, they get them all. That one hunter should drive all trespassers out. I'm not advocating giving them free reign. But, if the conversation is cordial, you could offer retrieval rights for their time and effort preventing others from crossing the "fence". Just a thought.
And, you are correct. If you go in with the stay the he!! off my property "don't even face it with your stands" attitude, you just started a property line battle that may never end. Same with the tarp idea.
If the conversation is not cordial, then I advise finding a relative or friend to start hunting your ground.