That is fairly standard wording for barns--I don't board but have seen contracts for boarding and training barns and most--maybe all--include that wording (or very similar if not that exact wording) When we had Morgans we did stand a stallion to outside mares & our breeding contract included similar wording. Naturally we took every precaution to ensure that nothing did happen to the visiting mare, just as we try to make sure nothing happens to our own horses. However, as you know, with horses anything can happen no matter how hard you try to keep them safe, and barn owners do need contract wording to protect themselves in the event something does go wrong. Honestly, wording in a contract will not necessarily protect the barn owner from a lawsuit--some people would sue regardless, and might possibly even win if they could prove there was serious negligence on the part of the barn owner.
You need to ask yourself--do you trust the barn owner (and staff) to be careful with your horse? Or do you feel that the barn is poorly run and staff is likely to be negligent with things like fence repairs, keeping gates closed, etc.?
Using my own barn as an example--our yard is not all fenced. If a horse manages to slip through an open gate and get out into the yard there is nothing to prevent him from going out onto the road (not a busy road here most times--it is not a paved highway). I don't feel that makes my property a risk to horses. Yes, we've had horses get out but it is certainly not a common occurance and only once did the loose horses go out to the road (and across it into the neighbor's field)--once in 25 years that we've been here. Otherwise it's been only a single horse--and like I said that doesn't happen often--and that lone horse stays in the barnyard around the other horses that are still in the corrals. We have an extremely low incidence of injuries in our horses--the property is safe for horses and we give extremely good care regardless if it is our own horses or someone elses (not that we often have outside horses here) As a barn owner we don't want an outside horse injured any more than the horse's owner does! If a visiting mare had ever gotten injured here it almost certainly wouldn't have been due to any negligence on our part--and if the owner wanted to sue anyway they'd have no luck in proving negligence. But, like I said, with horses things can just happen through the fault of no one other than the horse's aptitude for hurting itself "somehow" and that is why barn owners include that wording.
If you don't trust the barn owner in question then you should certainly look around at other facilities, but be prepared for those facilities to have the same wording in their contract. And if a barn doesn't have that wording, or doesn't have a contract at all, don't assume that makes the barn safer or that it means the barn guarantees nothing will happen to your horse while it is there.
