I live in an apartment complex, so when I take Fin out he is always on a leash. I use one of those retractable leashes so I can let him run on the grass. I keep it so that when we are on the sidewalk the leash is short and he's right beside me. When we're on the grass I let him run with the leash long. He does pretty well when walking on the path, but sometimes he starts to pull so much that he's choking himself. I don't want to give in and make him think if he pulls hard I'll let him go, but I also do want him to make himself pass out. Any suggestions? Am I sending him mixed signals by letting him free sometimes and not others?