I agree with most everything said here so far, and would proceed to follow the suggestions made above, like the signs, showing that you are losing money via lease ( if you sue ), cameras, etc. I will add the following from my past experience so it may help.
Call the police as soon as possible. Do not hesitate and say "the next time". Game warden sounds good if they will come out, but in my area the police will start a case. I put signs up around my whole property as was told to do. They kept tearing them down. Every time I called and reported it so to build a history. It was impposible to keep them up, but the police eventually said that when I do catch them, at least there is a record of me trying.
When they were finally caught, I did prosecute. There was no cost to me, they took care of all the details/work. The police here find it very frustrating when you don't follow thru after they have tried so hard to help you. This was difficult for me to do, because you don't want to cause friction. But, since then, I have been left alone. Wiord travels fast. I do think that in time, more will come but you have to stand your ground.
Alot of this was a result of seeing my dad with the same problem for his whole life. Tresspassers coming, him catching them, calling the police, let go with a warning. Not long after, they were right back stealing, vandalizing, etc. My dad didn't want to cause problems, but it was a never ending problem to him. So, I am trying a different aproach.
Cameras are a great tool., but they are costly when they bust them up. Most will, if they find out about them. I took to putting a camera inside a box that looks like a bird's nesting box. I would then put alot of these boxes up all over. Most didn't have anything in them, but it took time on their part to figure out which ones. You might even start putting a few of these up now, so if later you put a camera in one, they will not be so suspicious.
