Long reining is a technique in which you drive a horse forward using two ropes, one on each side. It is a traditional preparation for training a horse for carriage driving, but it is occasionally useful for encouraging the horse to go forward with the trainer behind and for getting him used to rein aids. Unfortunately, long reining is very difficult to perform well because it is difficult to keep the rein contact light enough. It should therefore be practiced only with the greatest care, and only by a very experienced trainer. As a consequence of poor long-reining technique, many horses have mouth problems or tend to unnaturally shorten their necks. When teaching a horse to long rein, start off with someone leading the horse on his left-hand side while you attach one long rein to the same side. Once the horse is settled, the rein can go through the ring on the side of the roller, which stops it from dropping down too far. Then remove it and do the same thing on the other side before introducing both reins. Long reins should be approximately 33 ft (10 m) long, lighter than the normal lunge rope, and with no handles on the end. If a horse gets loose when being long reined, the two ropes tend to “chase” and frighten him.