Greyhounds are notorious for slipping out of collars, so I use a special martingale collar also know as a greyhound collar. It is the only collar I would ever use on my greyhound. If I ever get a doberman or similiar type dog I would use this type also, it is similar to a choke collar but has a loop so that it doesn't completly go closed. It is the only type of collar I would by for any dog.