In my neighbourhood there is a very little park which isn't fenced but is surrounded with trees. The traffic around the park is minimal to non-existent. My intention is to teach my dog to stay within the perimeter of the trees when I'm playing with him there. Of course I will keep the leash on him but I want it to be a automated reaction to not go on beyond the trees even when the toy lands there If I tell him its not safe. Its probably a unnecessary safety precaution in this case but I think it would be a good thing to learn my dog as its probably useful in other less safe places. Can anybody tell me how I would go about teaching this to my dog?