SP. if you haven't done so already, call the DNR (or have your Dad call them) and tell them someone was poaching on your property, and that you want an officer to come out and talk to you (or your parents) about it.
That's the only way that you will get anywhere. Let us know what they say.
May have to find out which law enforcement agency handles these things.
This is more akin to livestock theft than poaching. Do they still hang rustlers?
I agree that you need to get the officials involved as soon as possible, and as many times as you need to.