Pondered a bit about what to do next. Putting up more signs, more robust signs placed higher and thus harder to take down is one option. But the thought occurred to me that if there are no trees/forest, then there will be no game worth hunting and thus no real need to worry about trespass/poaching.
So contacted 2 local (there) timber companies to see about selling off the timber on the 35 or so acres which of course will clear the land and me getting a bit of cash out of it. Not a simple process I am sure but one that may just solve the problem.