Standing in the stirrups or doing your two-point position all while really pushing your weight down will help you to get used to the feeling of having your heels down all the time. Eventually your muscles should be able to remember this feeling and you will find it much easier to do so - it's not something that comes easily and some are able to flex their heels more easily than others! Remember, we are asking our legs to stay in a very unusual position while riding, so it's understandable that it will be hard thing to master!
If you can't ride all the time you can also practice on some stairs. Stand facing the steps (you may want to use the lowest step.... Hahaha) and put the balls of your feet on the step. If you have to, grab a hold of the railing or wall, bend your knees a touch and slowly lower your heels.
The first secret lies in spreading your toes apart - which allows the ball of your foot and arch to stay really flexible which then allows your heel to drop. You have to think of those pedicure sponges between your toes!
The second secret is to keep your KNEE cap pressing straight down, like you are kneeling - drawing it straight back towards the horse's hock and THEN stretch the BACK of your CALF MUSCLE down, which will in turn LENGTHEN your heel all by itself, without you forcing it down.
I've heard different things about those Sprenger stirrups (and similar ones, ie Royal Riders). I have ridden in a couple and found I lost my stirrups all the time with them as I tend to over flex my heels as it is, so with those stirrups I would flex even more and my feet would just come flying out!
I'm not sure that's a very common problem though.
I like the way Linda Weldon ^ described the mechanics of putting your heels down.
I like and agree with all the suggestions submitted here's something else to try: Get a couple of bean bags and ride around with those for awhile. Bet you can't do it at the trot>>>You need to retrain your muscles and ligaments for this position again. I find visualization and thinking in different terms (ie. toes to the sky) helps as well. Position is a big thing so keep reminding yourself with imagery of a sting being pulled straight up to the sky out of the top of your helmet, this seems to help remind us that with that our toes also can be pulled by strings to the sky. I'm sure you've heard of these in your beginner lessons but it is always good to refer back to those simpler times when our heads weren't so full of the more high school details of riding.
WOW what a great idea for begginer riders! I teach a lot of first time riders and once we get to the trot teaching them to really keep there heels down is a difficult. Going to go tomorrow to the Dollar store and buy a few little beanbags. Will also make it a fun game outta it. great idea!
One thing that might help you with this is stretching, especially your calves, before riding. I know it might be embarassing, do it in the bathroom if you need to. Stretch your calves (you can look up on google for calf stretches) before and after you ride. Having tight calf muscles makes it a lot harder to bring your heels down! =]
when we get students that don't keep there heels down is we place the stuppus in a weird angle where your baby toe is and place the stuppup so it angles sideways the left from the angle to just before the center of your foot it angles your foot so your feet are straight and its more comftorable to keep your heels down.
Our 4H instructor was big on that haha but hope it helps when i started English i'd been barrel racing so much it didn't matter but once i got my english saddle dusted off it was big time heels down and i've been doing so much both western and english and that method helped me keep my heels down either that or my instructor telling the kids that your toes up meant your horse would go one way and youd go the other or heels down and your horse would go one way and youd move with them hope it helps