I have never heard of locking a stall. That's.. scary for me.. I have a quarry beside me and they blast dynamite. The first time they did it I thought it was an earthquake. My barn DIDNT come down (not even close) but I ran and threw my horses out. Just quickly opened stall doors and let them go. ( everything is fenced) had the stalls been locked and GOD FORBID the barn came down they would have all been crushed. (now when they blast they come over and politely tell me so im not riding and so the horses are out) the don't bat an eyelash at it anymore..
PLUS! Im sorry, but my horses are only stalled during the day if its freezing rain and very slippery. (canadian climate
) theres no reason for a horse to be stalled that long unless because of injury. Its a good recipe for disaster IMO