We had a very secure, custom built, loads of money spent (not by me but my employers) stable block, fields, kennels etc. The stud that our Arabian pure breds came from was about thirty miles away. Their yard was the location for a highly structured rustling operation. It was not the cameras, the infra- red beams or any of their security measures that saved their much loved and very valuable stock...it was their Yorkshire terriers!!! They phoned us at three in the morning to get us to take all head collars off and bring horses in the fields into the stables. The police found the horse thieves but the lessons were never forgotten. All horses, at home and at the stud were never left with head collars on again.
Why make things easy for theives? Even when you have the best security in the world determined thieves will have studied your systems and every extra second counts.
No horses were taken, by the way, but several horses had been led by their head collars into the yard before the thieves ran away. Two were tied to gate posts with the thieves belts.
We still used head collars in the day time when someone was around but every horse, pony and cow had them taken off when left alone.