It depends what state your in , each state has different laws that prohibit people from going onto your land. In NY where I'm from it's illegal to tresspass without written permission from the land owner, now don't get me wrong there are some loop holes, but for the most part the DEC will fine them and or arrest them. Any municipality can arrest someone if a complaint is filed. It is NYS Law that the person tresspassing must give the landowner or the agent in charge of the land his backtag number and his full name. You could try posting your property if possiable. Any law enforcement agency must provide service to you, whether it's fish and game or others in your area. Try to get the name of the person or a licence plate off their vechicle any info would help. Usually the first time someone gets arrested they spread the word that you are not playing around and don't want people on your property after all your paying for it and you have the right to keep people off your land. Ultimately it is immpossiable to keep eveyone off your land but as soon as people hear your having people arrested for tresspassing it should slow down a bit. Press charges it's all you can do. Do not get into violent confrontations with these people, if their that much of a scum bag to sneak onto your land you don't know what their capable of doing, protect yourself and your investment. Good luck