On a busy city street in downtown Boston, a police horse steps on an unsteady manhole cover as he trots along. The horse scrambles, loses his footing, and his hind end disappears into the manhole. Or, you have to train in this cement-like arena two days a week. You don't want to risk wearing his shoes until they are paper-thin. Carrying a rider on any hard surface is a tough job for a horse.
Hard surfaces come in many forms.
There's that parking lot where you lunged your horse last weekend at the horse show. There's that cracked-clay pasture where your horse was turned out all last summer. And then there's that concrete pad outside your barn, where all the horses stand, all the time. You don't have to ride your horse on a tarred road to risk concussion injury. In the back of your mind, you know you might be overdoing it.