I ride a horse at another barn with ex racehorses. I took a lesson on the one and hadn't been on him for close to a year. My instructor took us into the new arena where we have to work from now on. I'm still on the lunge line at her place with no reins. The horse I ride doesn't have a long enough mane to hold onto, and so now I'm used to gripping to the front of the saddle. My main problem is that this horse likes to break into a canter when we're trotting, which really throws me off balance when I have nothing to hold onto but the saddle and that doesn't help at all. So yesterday at my lesson I ended up falling off once and almost two other times because he keeps cantering. How can I prevent this from happening with no reins and no control over the lunge line?