How do you start to teach a puppy (12 weeks old) to heel? We've read that they should walk on your left, but what a laugh.... Brontie darts from left to right, back to front, round in circles, stops, starts, etc. What's the best way to start teaching her to walk on the lead properly? And are extendable leads a bad idea in the beginning? Don't really like them but at least I know she is safe!