When you first learn to canter you’re taught to ask in a corner because it helps to put your horse on the correct lead. Once you’re more confident make things harder by asking for canter at E or B. Without the benefit of the corner your horse may give you the wrong lead.
The correct lead feels comfortable. The movement rocks you from back to front like a rocking horse. When it’s wrong the movement rocks you from side to side and can be almost impossible to sit to.
Some riders can naturally feel when things are wrong. If you can’t don’t worry. Look down at the shoulders. The leading (inside) foreleg moves on its own. It stretches further forward than the other to help your horse to balance. When you’re correct the inside shoulder moves further forward than the outside. It takes time to see it. Practice cantering round the school. The more you practice the easier and quicker you’ll spot it.
Just to complicate things horses can also canter disunited. Instead of a diagonal pair, one side of legs move together. In this case the inside shoulder may well be moving further forward than the outside but the canter still doesn’t feel ‘quite right’. If in doubt, trot and start again. It’s not the end of the world to be cantering round the school disunited or even on the wrong leg but it will certainly make your life more comfortable if you get it right.
Riders often slip to the inside when they ask for canter. By using your inside leg to ask him to strike off (see The Perfect Canter transition) you should be sitting squarer in the saddle. To make sure put a pole on the inside track opposite E or B. Ask for canter as you ride past. Lean to the inside and your horse will strike off in that direction – as if he’s going to start a circle. The pole will make you more aware of it.
How quickly can you tell which leg you’re on? Test yourself by asking for canter on the centre line. Look straight down the centre line and be clear with your aids. Have faith in your horse. Ride the transition exactly as you would in a corner. There’s absolutely no reason for him to give you the wrong leg.