My suggestion is to start posting signs saying no trespassing, as well as poaching will not be tolerated so everyone is notified. Also, inform your local police department or county sheriff that this is going on and to see if they know anything about it. After that, post a seperate camera (without flash) in the area and see if you pick anything up, but since you know its happening, the only thing to do is to post up on the weekend and see if anyone drives by. If so, let them know this is not going to happen in the future or the athorities will be called out to handle the situation.