Going in a straight line for a horse is not as natural as you would think
. They need to be taught how to do this, especially if we want them to perform a dressage test. A straight line comes from going forward with impulsion, and it is this 'forward and straight' phrase that all schooling, dressage and lateral students will be very familiar with. This is one of the most essential building blocks of good schooling; you can't have one without the other.
The horse needs to be channelled by both your hands and legs. You will need to use hand and leg together, legs to provide impulsion, hands to keep the pace and both supporting both sides of the horse to prevent him from falling out either side and keep his body straight. All of us must be familiar with a horse falling out through their shoulder at times. A useful technique to help with the line you choose, once you are aware of how to keep the horse on this line, is to pick a point in the distance, look at it and ride towards it.
To begin with it can help working along the straightness of a fence line but this does not bode well for future development as it is very easy to become lazy with your outside leg. Other schooling aids can be worked on to help the horse understand the pressures applied from either of your legs when trying to support the horse in a straight line. Turn on the forehand and leg yield are good for this but will require a sound knowledge of how to perform these in order to get results. To get a truly straight line you need to work and apply both sides of your body to channel your horse.