Don't let either of them "help" bring in the mail...
I noticed that Rock seemed particularly interested in a thick tool catalog, so I said, "You want this?"
I threw the catalog at his feet and he promptly scooped it up in his mouth. First, he had fun ripping the pages. Then he liked flailing it around and hitting the other horses with it. Eventually, he did something useful and began sweeping the barn floor with it.