One Foot In the Stirrup - Advice by Trainer Christy Mellington
I too have ridden horses that will accept everything gracefully until you put your foot into stirrup to mount. When I encounter this problem I have found that hobbling works really well. Hobbling teaches a horse to stand in one place without freaking out about what is going on. The horse then tends to focus on what it already knows; and learns to accept new, even frightening things without running away from the situation.
A horse must be taught correctly to hobble. Begin by haltering the animal and attaching a lead rope. Using a separate cotton lead (as this will not cause rope burn) wrap the center of the rope all the way around the pastern (ankle) of the left front foot and bring the ends back to you. Now, by simply applying a little upward pressure teach the the horse to lift its foot. Once the animal complies, release the pressure and allow it to put its foot down. When your horse understands that giving in to the pressure provides release, take a step sideways and lift the foot while guiding its step toward you.
Teach the animal to lead by its front foot by applying pressure to the rope in your direction. When it takes a step, release the pressure. By inducing your horse to first take a step to the side, it will make the lesson more easily understood. Once these lessons are learned; you can then lead forward. Repeat on the right side. Take your time and make certain your horse feels confident about leading by both front legs before you move onto the hobbles.
If you have a small horse, I recommend using leather figure 8 hobbles. These hobbles are easy to apply, easy to adjust, and are strong and safe. I prefer the Weaver brand.
The first few times that you outfit your horse in the hobbles, apply them right below the knees at the top of the cannon bones. This will prevent harming the pastern joints should your horse decide to fight the hobble at first. Also, find a place with soft ground just in case it stumbles.
Put the hobbles on and say "whoa". Apply slight pressure to the lead, and encourage it to attempt a step. Once it makes the attempt, again say "whoa". By this time your horse should have figured out pretty quickly that it is unable to move with the hobble on. When you feel that the animal is confident in the hobbles, it is safe to apply them correctly at the pastern joint.
When your horse fully understands that it cannot move in the hobbles, try putting on the saddle while the animal is hobbled; instead of tied. If it accepts this, you will more than likely be safe attempting to mount.
Have a horse savvy friend hold the lead rope while you are attempting to mount. Do not just climb on right away. Make sure that the horse accepts your walking up to it, putting your foot in the stirrup, and stepping up and down. Do all of this in a calm, relaxed manner. Also try standing in the stirrup and reaching over to pet the animal's right side, before you sit down in the saddle. Be patient. It may take a few lessons spread out over a period of several days, before you see results.
When your horse confidently stands several times for mounting while its feet are hobbled, it is time to take the hobbles off and ride!