I haven't been riding long but I'm having trouble keeping my heels down. My heels are quite high at the walk and trot but now that I've just started cantering my feet seem to keep slipping through the stirrups, which I think is because my heels are too high.
I know this has probably been posted a thousand times before but any advise on stretches or exercise that could help would be much appreciated.
Stop thinking of it as "Heels Down" and start thinking of it as allowing your heels to be your anchors. It isn't about pushing your heels down, it is about allowing your bodies weight to absorb your bodies weight - that's it. It doesn't matter if your heels are down at a 90 degree angle, 45 degree angle or a 10 degree angle, just so long as they are able to do their jobs..which is anchoring you in your tack.
You have to allow your bodies weight to naturally flow from your head, into your seat, and from your seat, down into your lower leg and heels. You cannot grip or pinch, the moment you do that, you block that natural weight flow from occuring.
There is also another factor into allowing your heels to do their job - proper foot placement in the iron. Proper placement will allow your ankles to soften, which will in turn, allow your heels to do their job. The balls of your feet must be on the base of the iron, where the outter bar is at your pinky toe, and the inner bar is at the ball of your big toe.
Then, there is proper toe angle - you should have at least a 45 degree angle, where the correct placement of your calf, is making contact with your horses side. You don't want toes completely forward, nor do you want your toes out beyond a 45 degree angle, you want to find that sweet spot where you can solidify your lower leg.
Once you have achieved your lower leg - knee softly making contact with your saddle *Even placement from your thigh to knee* opened where your bodies weight can flow naturally. Proper placement of iron on foot, allowing weight to dispurse through your ankle, and contact on horses side with your "sweet spot" of your calf.
The moment you grip with your knee, you block that flow. If you feel that you are reaching for balance in your toes - you've lost your solidity. Stop and re-establish yourself. And start over. You'll get it :)