If he were my dog, I would do lots of left turns. I would trot, then slow down and turn left immediately. Yes, I might catch him in the shoulder with my knee, but consequences are the only language we have with which to communicate. Words don't work. You want your dog's front feet to walk in step with your feet. That way he can move out of your way when you turn left, by slowing down a bit. He can speed up when you turn right. Leading (being a little ahead of you) is a safety hazard, because you could trip over him in a sudden left turn. So work on it a controlled situation. Lots of praise when he gets it right!