I say definately a harness, we never take them out in a public place without a harness, actually they have their collar on with the harness and three tags. It sounds like overkill but it works. They only wear their collar at home but we add the harness when we go somewhere. One reason for that is each of our three Schnauzers backed right out of their collars and we were left holding the leash with an empty collar and chasing them down.LOL
Jackie