I agree with Airborne. If your not around it much, trail cameras are the way to go. I'm in the same boat you on property. We had alot of trespassers the first couple yrs owning it. We had to keep on them, we started taking back tags, names not knowing whom they were. We called the law a couple times. Then we put trail cameras up, and got a couple that way.
I'd also recommend not letting them know you are there. For example close up your gates once there, hide yourvehicle.
You can also go to your closest NY State Police barracks, and ask to fill out a patrol area form. Explain your problem, and once you fill out the form NYSP has a reason to specifically patrol your area. Also ask for their personal State Police Patrolled trepassing signs to post up. They are usually real good about this. It gives them a reason to patrol new spots!
Eventually the word will get around your serious, and they should back off. Least if they have any brains. If they don't you'll catch them sometime, and prosecute. Good Luck.