Note: This trick is not applicable to the Wolf clan. Train a horse by locking it on your stable. Then, let it out by using your Peasants. Click a unit and place it near the stable. Then, bring your horse back to stable. Click your unit, and while the horse is walking towards the stablem double right click the selected unit. If done fast enough, your selected unit will ride on an invisible horse. As you can observe, that horse is free.