Just a few months ago on another forum, a lady lost her mare and foal, when they ran through a barbed wire fence, when being chased by a loose dog which got into the pasture. Devastating. Keeping ANY stallion within barbed wire fencing, should be illegal. Stallions are notorious for jumping fencing to visit mares or just go looking.
I'll bet that all those who have lost a horse or have had to deal with a horribly injured horse because of barbed wire, also said before the incident, "Oh we've had barbed wire for years and never had a problem."