I don't recommend buying a collar. You can if you want, but if pulled to hard, a collar can collaspe a chi's trachea. i recommend a harness. chico is about 8 1/2 pounds, and he's kinda buff, so he wears a medium harness, and i have a small leash, one of the ones that can go up to 16 feet in length. it gives chico a sense of "freedom" on our walks, lol.