Or REALLY good hunters. NOT haunters. Hunters. Deer season is right around the corner, and any decent hunter is also a decent tracker. Put out a plea on craigslist or do some word of mouth, and see if anyone with half a brain is a good tracker. Maybe you have someone in your family that deer hunts regularly and has to follow a blood trail to get their kill in the morning, and maybe no one has thought of applying that method to finding out how these guys are getting in.
And if you can afford an off duty officer. You can afford a few dozen halogen bulbs and light up the perimeter of your property. Hell, put them on a motion sensor. That'll get the schmucks!