close, lock, etc. the stable door after the horse has boltedidiomPart ofdoorclose, lock, etc. the stable door after the horse has boltedclose, lock, etc. the stable door after the horse has bolted — idiomidiom1. To try to prevent a problem after it has already happened.1.idiomDefinitionTo try to prevent a problem after it has already happened.ExampleInstalling a security system after the theft is locking the stable door after the horse has bolted.Apologizing now is like closing the stable door after the horse has bolted.