Teaching a horse to "pat the ground"
I spent yesterday at Capital Challenge watching some lovely lovely horses go around. Despite the caliber of riders, there were very few who had all perfect distances, rather they all had workable distances out of excellent rhythm and jumping efforts that were beautiful almost no matter what.
Some of the distances ridden were quite deep, and it appeared that the quality of the horse's jump really depended on its ability to stay really light and balanced in that last stride, to pat the ground, and those that succeeded had a great jump despite the deep or quiet distance.
So what are some specific exercises to teach a horse to stay that light and balanced in the last stride or so and maintain its jumping form? I'm looking for exercises beyond the obvious of shortening and lengthening in the gaits.