Somewhere in most horses’ training, usually when they are still green, they have trouble picking up one or both canter leads. If that happens to you, try using leg-yielding to increase the size of a circle to solve this problem.
This exercise works because it increases the flexion and bend, and horses will pick up whatever lead they’re bent and flexed toward. If you’re tracking to the left and your horse keeps picking up the right lead, chances just before the canter depart, he throws himself into right bend and right flexion.
To ask for the leg-yield to increase the circle size, first spiral onto a smaller circle – 10 or 15 meters.
Then to start the leg yield, shift your body weight from your inside seatbone to your outside seatbone if you’re sitting the trot, or from your inside stirrup to your outside stirrup if you’re in posting trot. That difference in your body weight tells him, “go sideways,” as opposed to just staying on the circle.
Also, be sure to look where you’re going as you leg-yield out to increase the size of the circle.
While you’re still go sideways, sit the trot for a stride or two while blending in the aid for the canter by brushing your outside leg back once like a windshield wiper-like action while you’re still going sideways.
Keep your inside leg on the girth to support the bend. If you’ve kept the bend while going sideways, he should pick up the correct lead.