I'm new here, and not fully aware on the procedure on posting. But, I have had a lot of luck with just one simple trick. Take a good hold on the outside rein, provided you aren't using a solid bit, and gently reprimand the horse, by putting it back in place with the outside rein, every time it pivots on you. Horses hate being corrected, so be prepared to spend a while if necessary, and win the endurance game with your horse. Good luck.