Our RDA group used to use a school that had cut up carpets as its surface. Not only was it very deep to walk on, the group stopped using it when it was noticed that there were bits of chopped up metal carpet treads in it! When the yard was sold on not that longer after, the new owners had to...
Playing Devils Advocate here - aren’t horses living a lot longer and in work for longer nowadays though? Back when I started riding 15 was pretty ancient for a horse. All I see now are ads that have horses for sale that no one would bought years ago as their working life would be practically over.
My one experience of it was letting my horse be used for a RC demo. He wouldn’t move over when asked (would lean into to you instead). The instructor’s suggestion? Poke him with a hoofpick until he moves!