Develop a lesson plan with many steps where your horse can give you "yes" answers. If you ask the horse "can you go left?" the horse has to guess the answer.  He will not always give you the correct answer until he has made several wrong attempts. Set up the lesson plan so he has choices with the "yes" answer as one of them.  By process of elimination, the correct answer will be selected. As a teacher, realize the correct answer is always more obvious to the teacher than it is to the student.  Continue to repeat the step until the horse has it mastered and will give you the correct answer 100% of the time. Then you can go on to the next step in the lesson plan toward your goal.

Once you have achieved your goal you must practice it continuously to maintain that level of training.  If your horse does not respond correctly at any time after you have taught it to him you must go back in your lesson plan to a step that the horse does give you the correct answer and YES teach it again.  This time it will not take as long to teach.  "DO NOT SKIP ANY STEPS!"