Im starting to teach my horse how to neck rein, and my strategy seems to be working. When I first started, I would plow rein, say I was turning right, so I would plow rein with my right, and let the left rein touch her neck. I would also press my two fingers on the left side of her neck to make sure she felt it. She's starting to neck rein now, after about 2 weeks of working with her.