If you've posted signs and had a locked gate, I'd say good on ya. If this is a case where you did it right at the turnout, I'd say probably not a good thing, but given that you've 1--been ripped off before, 2--filed the proper reports, 3--the Keystone cops haven't found anything, 4--put them well inside your property, I say let them try to sue you or file charges.
See, this is where I like NH law. Not only are they subject to deadly force if they're in your house, they're subject to it ON YOUR PROPERTY.
Too bad you didn't catch them as they were going by and turn them in right then. Then the cops would actually, I dunno, DO THEIR JOBS?