Hi, You are a Horse owner, you must be knowing much more than me i am sure. But with my experience from childhood which i am practicing till date, a animal works on instincts & energy shared by its leader, So are you a leader at the moment? What do you visualize is going to happen after you mount him is what he is going to give you. So what is it that you picture that you create, is it frustration of knowing that he isn't going to move or is it anger that today i will make him move? As i said earlier you are the horse owner so you have to become a leader, serene and firm, with it practice patience & create a pretty picture before you try and mount him again. I am sure you will achieve your goal.