sounds like you should look into Run and tie, They have it at Foxcatcher. You have to look up the details but the basic is 1 horse 2 people and a 25-40 mile trail. Rider A and horse take off riding, while rider b runs. After a ways, the horse gets tied up, and Rider A takes off running. Rider b catches up to horse unties gets on horse rides passes rider a a ways, ties up the horse gets off and runs. So basically all three parts of the team go through a run/rest cycle.
But ummm, ee gadds running ten miles makes me hurt thinking about it.