Chemaine Hurtado, owner and trainer at Symphony Dressage Stables, has a good tip for picking up the counter canter. She suggests cantering out of the arena. In other words, if you're on the rail, position yourself so that you could actually canter out of the arena if there were room. It's a great visual to get your seat and aids in the correct position for a change of lead.
When we couldn't get it on Tuesday, I scrapped the serpentine and did lots of simple changes to work on his balance. When I ride today, I'll go back to the three loop serpentine, but I'll start them very shallow to see if that helps Speedy loosen up a bit.
Chemaine also gave me a couple of other tips: open my outside rein a bit to draw his shoulders around; bring the outside rein back a little to keep him sitting (like in a turn on the haunches; and finally, push his haunches around to sort of pivot his body in the direction I need him to go.
I'll keep you posted.