Join Date: Dec 2009
Location: Cincinnati, Ohio
If you drop your stirrups, where do they line up with your foot/ankle? I always follow the ankle bone rule to start (bottom of stirrup hits ankle bone), then adjust from there. Now my stirrups are 2 holes(ish) lower than that, but it's taken work to get there. If you're feeling like you have to reach, try shortening your stirrups a bit and work back down over time as you feel more secure.
Following others, it does sound like there may be more issues going on than just too long of stirrups. I used to lose my stirrups all the time due to pinching with my knees, or gripping with my legs, so that's a possibility. It kind of sounds like you might need to focus more on getting your overall seat/position more secure so that you have a better chance of keeping it when you focus on something else.
Without seeing what you're doing, it's hard to give you something specific to help. My recommendation would be to try and pinpoint what it is physically that's making you lose your stirrups. If you can video yourself, watch how you ride. Focus on you and not the horse for part of your ride, and then focus on the horse as you do when you normally ride so you can see the differences in what you do (if there are any LOL).
Hopefully that helps even a little, and I'm hoping this all makes sense. It's late and I'm tired, but it all makes sense in my head! :)