This is such a useful exercise to advance a horse’s training. In order to progress you must be able to use your outside aids effectively – think of the half pass where the outside aids coax the horse to move into the direction of the bend rather than fall away from it.
When training young horses we teach them first to move freely forward and rhythmically and then introduce lateral work - usually starting with leg yield - teaching the horse to move away from the inside leg in a bend - but we also then need to show him how to be “contained” by soft outside aids.
Riding a square off the track means your outside aids are responsible for keeping the horse straight and turning him on the corners. If you ride the square on the track it is likely that the horse will simply “lean” on the wall and you will pull him round the corners with your inside hand – not what we’re trying to achieve! So be strict with yourself and stay 3 or 4 metres off the wall. Begin in walk and as you get to the corner, look and turn your body around it – stay sitting up very straight through your torso, don’t collapse. Keep your weight down your inside leg and gently use your outside leg and both hands as a pair - keep your hands low, and imagine you are turning the chunk of his withers and shoulders – to turn the shoulders around the corner. The neck and body of the horse will stay fairly straight – it’s more as if he is pivoting around his back legs. Of course the corner will be more curved than appears in the diagram, but try not to let the horse fall out towards the wall. Then ride straight. On the straight sides make a conscious effort to look up and ahead, not at your horse with your body weight and rein pressure totally equal and symmetrical. Then – another corner.
When you can do this on walk on both reins with no loss of rhythm then try it in trot and canter. You may want to make the square bigger, but do try not to end up just relying on the wall to turn the horse rather than your outside aids. In canter it may be easier to do a rectangle just off the track using the whole arena.
Do work on maintaining a nice easy rhythm during this exercise – it can be easy to get a little tight and ruin it, remember no movement is worth losing the rhythm for. When the horse can do this easily with a fairly straight neck and body, add in a little flexion.
When you are teaching the horse new things, a good trick to keep your riding harmonious and subtle is to imaging you are being watched and want to make it appear very, very easy and fun!