I would simply place a note back on the camera saying something along the lines of.....
I believe you are istaken this is my own private property. I would appreciate a call at ***-**** so we can get the matter resolved. I kindly ask you to remove yourself from this area. I do have pictures of you from the note that you left me before and if anything happens to my stuff, I will take it to the law.
Thank you and happy hunting just not on MY LAND!!