I personally had the pleasure of working with Buck Brannaman on this very issue and I'll share what he told me. I was riding with a group of riders and my horse refused to walk and would only jig. The more I pulled on the reins the worse she got. He told me to one rein stop her until she could be controlled at the pace I chose. Everytime she insisted on that trotting, I was to pull her head to my knee. He said, quote, "I don't care if you have to ride her that way all day, you do it until its easier for her to do the right thing." And I'll be darned if it didn't work! It took all day and half of the next, but she got it. He was a brilliant teacher. I spent 4 days riding with him and it changed how I ride forever and I use his principles daily.