How can you keep your legs still when rising to the trot?

You can keep your legs still at a posting or rising trot by squeezing with your knee calves. If you squeeze with just your knee calves, from there down to the stirrups it should be still. Unless you have a horse like me where you have to bump him in a rhythmic motion to keep him at an extended trot. So the answer is to squeeze more with you knee calves instead of using your feet to post.