Given most shots on deer would be expected to exit the animal, is any shot taken on a deer right at the boundary of your permission a bit dubious. I'd expect it's almost certain the round would exit, cross the boundary and land on the neighbouring ground. I'm assuming here that the shot is otherwise safe, i.e. there is a suitable backstop, but thinking of the proverbial situation where the animal is just on the 'right' side of the fence. So, the deer is in the right place but the backstop isn't!