ive got a couple of suggestions. One would be leave the guy a note, with your cell number and ask him to call you. Get him on the phone and tell him you know its public land but since youve both taken a liking to same spot, possibly you could work together rather than possibly mess up each others deer season, work out times where each of you could hunt it, who knows you might end up with a good hunting buddy out of the whole thing.
other option would be to map out where and when hes going to come in and try and use him as a driver, set up some spots down wind that he may push the deer he spooks as he comes in.