Jake's a sheltie, too. We really don't have much of a barking problem with him. I don't know if it's because he's naturally not much of a barker or because of how we've trained him. Whenever he starts barking we remove him from the situation. For example, if he's outside barking, we bring him inside. If he's barking at a visitor we put him in the mud room. I think he barks when he's happy, and he knows that if he barks we'll take him away from whatever it is that's making him happy so he keeps his mouth shut. It couldn't hurt for you to try it.