I use the methods like MM and Cori mentioned. If they decide they want to walk off when I am mounting, then I will either turn them in small circles for a minute or make them back up several steps. Both work pretty well. Also, while you do need to be light into the saddle, like mls mentioned, I make it a point to be busy when I first get on. I get on, I'll change my seat a couple of times, wiggle my feet around, re-adjust my leg position, lean to one side or the other, etc, etc. If they move off during any of this, I will either circle them or back them up and start over. After that, I make sure that I give a very clear cue for forward. That will also help to keep the horse from confusing a small re-adjustment of your leg with a cue for forward.
Last edited by smrobs; 11-12-2010 at 05:16 PM.