I would call the Game Warden and tell him that not only were guys openly saying they were going to trespass but also threatened you. I am not one for lawsuits and calling the cops on small things, but this sounds like it could be nasty. I would call them and at least document the conversation that you and those idiots had last night. Call the landowner and let him know the exact details of the call and if he still says you have exclusive permission to hunt. I know in alot of places here in Virginia,the landowner will give you a "permission slip" of sorts with his name and yours signed on the document so that if you are confronted by a GW, you simply pull it out and show him. SCREW those guys.