Tresper continues to destroy my stuff. What to do?

I had my land surveyed and put Posted signs up with orange paint around them. My little cousins are building a tree house on my land and this guy keeps destroying it thinking it is a Deer stand that someone is hunting out of. He also ripped down half my signs and is shooting onto my property. The footprints in the mud lead to his house but I never seen him do it. What can I do to stop him or at least get him to ask and clear things up. I don't want to go to his house because he could call the cops on me for going to his house. I live in Pennsylvania.