Last week I had a lesson with Tiny Clapham, and she suggested an exercise to improve the canter which I have never heard of before, but which worked absolutely brilliantly. After thoroughly warming up, you go walk to canter, canter 4 strides only (because the first strides are the best ones, the ones with the most engagement, and the horse hasn’t got time in only 4 strides to get too onward bound and on the forehand), then go back to walk, change direction in walk immediately through 90 degrees for a few steps (or more if absolutely necessary), canter again on the other leg, 4 strides, walk, 90 degree turn the other way, canter on the other leg, 4 strides, walk, 90 degree turn, canter, 4 strides only, and so on.
So, a zig-zag with right-angled turns, and alternate strike-offs.
It’s particularly helpful to do this exercise at 1 end of the arena, using the boards/fence to help you, so you’d do the 90 degree turn at A or C, and pick up canter towards the corner, for example.
It gets the horse really waiting and thinking and listening, and I found I needed to react fast to get the downward transition done well after only 4 strides. Before going in the arena I’d have a longer canter though just to convince the horse that canter is usually for more than 4 strides, because they soon start anticipating the downward transition after only 4 strides… which is good, of course, but they need to realise that you’re not always going to ask for that!
Caveat: it’s hard work, and I’d never ask a babyish horse to do more than a few of these, as it could be quite confusing as well as being so strenuous. The horse needs to already fully understand about going Forward at the slightest touch, as this gets them thinking of dwelling/waiting so much. But it is a very good concentrated exercise and you can really feel the difference in the canter very quickly, I found.