My bigger dogss were collars, but they are 25 pounds and up. Trixie who is 9 pounds wears a collar simply because she will eat or chew on the harness if you keep it on her. Scampers wears a step in harness all day that has his tags attached. I think if you were to use a breakaway collar for inside the house and a harness for outside or walks then you should be alright. Oh and I have bought a silk harness from Cindy and I must say that they are great and don't matt up the hair like regular harnesses, and it took him no time at all to adjust to it, with any other harness he hates it and it takes a long time to adjust, but with this harness he does not even know that he has one on because it is comfortable and light weight, the harnesses she makes are great!!
