If you buy land that you can't oversee 24/7 the best you can do to protect your valuable hunting land is ask the neighbor (and preferably the guy doing the poaching) if he would be the caretaker of your property in return for exclusive hunting rights. Seems counter-intuitive but now he won't let anyone else hunt the land and will take much better care of it. This way you will know who you're dealing with and maybe get him to change his ways. He probably poaches on other properties as well, so he may be willing to let this one grow bigger andf better game!