I understand your frustration, but I want to nip this in the bud as soon as possible. My complaint to the DEC was handled very much like yours with the officer explaining that there are really just a handful of agents in the field to respond to such complaints. He suggested calling the state police if a DEC officer was unavailable or calling the "poaching" hotline 1-800-TIPP DEC (1-800-847-7332).
I do believe that there is no way to completely stop trespassing. Even the best neighbor is not going to patrol every acre of your property in your absence.
It is the "problem" trespassers, those with no regard for the law, your property, or the ethics of a safe, legal hunting season, that need to be stopped. I can't stand by to let the total abuse of my land take place.
I know that threats and warnings mean nothing. Action needs to be taken to let these criminals know I'm serious. I will prosecute.