lock the stable door after the horse has bolted

lock the stable door after the horse has bolted

To try to prevent or rectify a problem after the damage has already been done. My father quit smoking after he was diagnosed with lung cancer, but I'm afraid he's locking the stable door after the horse has bolted.
See also: after, bolt, door, horse, lock, stable

shut/lock/close the stable door after the horse has ˈbolted

(British English) (American English shut, etc. the barn door after the horse has eˈscaped) take action to prevent something bad from happening after it has already happened: Last week all their silver was stolen; this week they’re putting in a burglar alarm! That’s really shutting the stable door after the horse has bolted.