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So, I'm riding this horse who is having issues with her left lead. She can pick it up because when ever I lunge her or free lung her she picks it up with no problem what so ever. Then I get on her and ask and every single time she picks up the right lead. For a while using an outside bend instead of an inside and asking on a circle worked like a charm and even she looked surprised that she picked it up. Buttttt good things only last so long and she seems to of caught on and now every time I ask for the left lead that way she picks up the right again. I keep trying to mix things up and make when I'm going to ask unpredictable as I can but nothing I try works. please helpppp!!! Oh she is also an ex-race horse who is trained in dressage if that helps at all.

Other than this she is the best horse ever! biggrin

If she picks it up fine when you're lunging or free-lunging her, I would look critically at your position and balance. Make sure you're staying in balance and helping her as much as you can, and not helping her by throwing your weight to one side. Not to say that you do, of course.
Saddle fit might be my next suspicion. Even if she's fine when being lunged in a saddle, the fit changes when you add the weight of a rider.

As for training, practice a lot of suppling exercises both directions and get her to the point where she can easily and correctly bend both directions at the walk and trot. Really work on improving her balance, and make sure she's very balanced when you set her up for the canter. You can also try giving a tap behind your outside leg with a crop as you ask for the canter, since the outside hind is the strike-off leg for the canter depart.

Good luck!

Thanks for all your help guys. Sadly she got into a fight with another horse in the field and has partially severed one of her tendons in her back left leg sooo we aren't going to be doing anything for a long time. crying