Large animals lean and rub themselves on corners and uprights, same principles apply to fencing. A thousand pound horse exerts tremendous pressure on these load bearing areas. Even if the structure does not collapse, many horses have been seriously injured or killed by impaling themselves on broken uprights or posts. Repair any structure or post weakened by their activities. Run your electrical lines in conduit and secure the conduit to the structure.
Horses are curious and love to pull or bite things to play while stalled.
Utilize encased outdoor lighting devices firmly secured. Interior finished walkways should be made of non skid material or finish. Gates and interior walls should be securely fastened to the structure or embedded in the ground. Look for gaps that feet and legs could be entrapped while rolling or pawing. All gates and doors should latch securely, but never lock a paddock or barn access doors, in most communities this is even regarded as an illegal activity.