I had the same issue with Riley. I walked him to the mounting block and went slow ...if he stood nice while we were stand next too it I steped up on it, if that went ok I put pressure in the stirrup...etc etc as soon as he moved I made him back up and do a few tight circles and we tried again. He soon learned it was easier to just stand there and let me mount. Posted via Mobile Device
I'm writing a book. When a horse won't stand still to mount pull his face towards you as you get on. He will circle and circle but don't release until his feet stop then get on. Wear a helmet. Repeat this process several times!!! Believe me it will eventually stop.
When you get on don't ride off right away. In fact sit there and let the horse make a mistake of moving forward or backward. For forward movement back him twice the movement. For backward movement back him 4 times the movement. Making the wrong thing hard and the right thing easy! Posted via Mobile Device
Horses are always looking for the easy way out of things. So if you make him move more than needed, he'll eventually figure out that life is easier-- and with less work-- if he just does what he's told the first time. But don't expect miracles in the first day. It takes time, and repetition. Just keep trying! And don't give in!