I learned a lot from all the excellent responses to making the leg stay put at the trot.
Like Bsms I'm a forty something rider coming back to the sport after years away. I've got a good walk and trot, sitting trot, doing nice circles, and can have a great canter. Unless the horse needs a lot of leg at the canter. If that is the case, my legss "scrunch up" (trainer's phrase!), my heels come up, the stirrup falls to my instep and I am a mess.
At my last lesson I asked her to specifically help me with this issue. She had lots of tips and instruction, but it seems my old unconscious muscle memory is just so strong. As soon as I need to squeeze at the canter, up go those heels.
I rode a canter without stirrups the other day and found my legs going way up and back without the stirrups. I could stay on like that, surprisingly, and I could fix it, but it appears to be a pretty strong habit!
Oh, and I ride hunters in Virginia, so we canter in half seat. This is not how I learned. Way back when, I learned to canter sitting in the saddle. It took me awhile to learn the half seat canter, and I think I can do it reasonably well as long as no extra leg is required.
So far my ideas to fix this are:
Tons of two point at the trot.
As much posting trot as I can stand without stirrups.
Bareback work, trot and canter.
Umm. Attaching bowling balls to my feet ...
Does anyone have any ideas for overcoming an old bad habit that is so ingrained?? I really like the idea of getting out of my conscious mind, but I think I have to get a new muscle memory in there first ...