“My canter transitions are great – it’s just the canter!”
“My horse goes into canter nicely but once he’s in canter it’s hard to alter the speed. He resists and hollows against my hand and seat if I ask him to slow down so any suggestions would be gratefully recieved!”
I did a Q&A recently about a horse similar so there’s a post here that might be worth a quick read.
Having said that I think yours is a bit different. The main thing is to remove the friction you’re getting between your hand and his mouth which is causing the hollowing.
You need to get him really coming back to you through your knee and thigh to allow you to just hold your contact without really using it to slow him down. There’s a great exercise here to help you do that. Although it suggests to ride canter to walk transitions at the end I’d try to just bring him back to the slowest canter you can do (don’t worry if it gets so slow it’s 4 time) and then allow him to go forward again. The whole aim of the exercise is to teach him – and you – that you can slow him down without resorting to your hand.
There’s a great exercise here that will get you both really focused on the canter and where you’re going. It takes the soul focus away from the fact the canter is just getting stronger and stronger.
I’ve used both of those exercises with a lot of different horses and you may need to grin and bear it for a few attempts but just plug away. Repeat and repeat and repeat – and then suddenly you’ll find yourself grinning because you’ll get a sudden feeling of control! At that point on the first go put him away and enjoy the fact that it worked! Do it again and again until you really get a feel for it; the exercise is such that he won’t anticipate and avoid it, it always gets results. If your thighs aren’t screaming by the end of it you’re not doing it hard enough!!
There are a couple of posts here that will give you something to think about as far as your contact and your position go – they’re great for that stage of riding that needs a bit of finesse!
Fingers crossed that something here helps.