Canter lead!

I can check if a horse is on the ridght lead in canter, it's just when I'm going around a course of fences it's really hard to check every time the horse lands after the jump! I have to keep looking down at the horses shoulders and my instructer keeps telling me to look up.
Any suggestions?

What would be really helpful for you to get a feel for your horse. That's how you get correct leads, proper lead changes, and blue ribbons at shows. I don't have any excersizes that would help, sorry :/ You just have to develop it over time. How high are you jumping?

90cm-1m :L
I ride once a week at a riding school but I might be going more often next term

You shouldn't be looking down to know what lead you're on. You should be able to feel like, like how you feel when you're on the right diagonal during a posting trot.
I wouldn't exactly know how to tell you or what to feel for since each horse is a little different but like Jumper said, you just gotta feel it out and ride and keep working on it. You could maybe go on a lunge line with your trainer and close your eyes and canter both leads and see if you can feel which one is the right one and which one is the left?

K i'll try that!

You should feel his hips pulling you to one side or the other. It helps to have someone on the ground to tell you if you're on the right one or not. When Sky is wrong, I feel like I'm being pulled out of the saddle like on those airport conveyer belts, lol..

I agree that you have to learn to get a feel for your horse. Pretend while you're sitting, that you're cantering on the left (in this demonstration) case. Move your hips to the left and forward then do the same for your feet. I'm sorry if this doesn't make sense but this is difficult to explain.

Looking down isn't a good habit to get into when jumping courses. A wrong lead canter should be easily felt. One of the main ways to tell if you are on the wrong lead is if your horse feels unbalanced. This is one of the easiest ways to determine if you are on the wrong lead.

I do have something that would help a little :)

When you are warming up and cooling down at the walk, doing nothing, think to yourself, "Left, right, left, right," Corresponding with the horse's shoulders. After you count 5 left steps, look down to see if you are right. If you are, really feel, and understand what that feels like. If you notice you are wrong, close your eyes, and try again. Then do it at a trot. After a while, when you are consistently getting it right, go to the canter and feel the steps your horse takes. Feel the long stride that you get to the inside.