Over time a gap can form between the shed and the ground that could catch a leg. The entrance to a shed depends on the stock. Two horses which get along can manage with a six-foot entrance. Otherwise, the shed should have an open front or two entrances, enough space to allow two horses to leave in haste when the boss wants in, or to prevent a horse from getting trapped and beaten up by an unfriendly herd mate. Remove fallen branches and tree stumps.
Horses collect puncture wounds in the oddest places from the most unlikely objects.
Water tubs and feed buckets out in the elements can break down and develop sharp bits faster than stall buckets. Drain pipes can have sharp edges or develop them over time as the ground around them erodes. Examine every inch of a new pasture. Ball admits that even veterinarians are not immune to oversight. Once, I was turning a yearling out in a paddock that had been used for many other horses.