My brittany spaniel, Sammy, needs some off-leash training. When he's on-leash, he walks pretty well most of the time, and when I let go of the leash, he's fine too, but when I actually take the leash off, he bolts. Then he thinks of it as a game, and stays just out of my reach. How can I train him to stay closer? I want to be able to let him off leash so that he can get more excercise, since he'd be able to run, but I can never get him to come back.