My horse cross fired and counter cantered all the time when I started working her. I lunged her for 3 months until she consistently took the correct lead at a canter. If she took the wrong lead or cross fired I would immediately drop her back to trot then canter again until she got it right. Sometimes in the beginning it would take 4 or 5 tries, you just have to insist that they keep dropping down and trying again. On a lunge line you can make the circle smaller so horse is forced to take correct lead to balance.