DT Systems pro and bird dog trainer George Hickox carries three items in every training bag: a clicker, e-collar and duck tape. The tape is for a handler's mouth. "When you repeat commands, you dig a hole you can't escape," he says. "If you say: 'sit…sit,' the first sit becomes meaningless to the dog. However, if he sits on the second command, you can't punish him for not performing with the first command; if you do he'll just be confused." Say a command once and enforce or reward appropriately.