lock the barn/stable door after the horse has bolted/is stolen, to

lock the barn 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 barn door after the horse has bolted.
See also: after, barn, bolt, door, horse, lock

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

lock the stable door after the horse is stolen

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 is stolen.
See also: after, door, horse, lock, stable, stolen
Farlex Dictionary of Idioms.

lock the barn door after the horse has bolted

Also, lock the stable door after the horse is stolen. Take precautions after damage has occurred. For example, After the burglary they installed an alarm system, but it's locking the barn door, or Deciding to negotiate now after they've been fired-that's a matter of locking the stable door after the horse is stolen . These expressions of action that is useless because it comes too late have long been proverbs in many languages and first appeared in English in the mid-1300s.
See also: after, barn, bolt, door, horse, lock
The American Heritage® Dictionary of Idioms by Christine Ammer.

lock the barn/stable door after the horse has bolted/is stolen, to

To take precautions after damage has been done. This proverb, found in many languages, first appeared in a French collection of ca. 1190 and found its way into a Middle English manuscript, Douce MS, by about 1350. It has been repeated ever since. Stanley Walker poked fun at it (The Uncanny Knacks of Mr. Doherty, 1941): “He locked the stable door while they were putting the cart before the horse.”
See also: after, barn, bolt, door, horse, lock, stable
The Dictionary of Clichés by Christine Ammer
See also:
  • lock the barn door after the horse has bolted
  • lock the stable door after the horse has bolted
  • lock the stable door after the horse is stolen
  • stolen
  • closing the stable door after the horse has bolted
  • close the barn door after the horse has bolted
  • close the stable door after the horse has bolted
  • shut/lock/close the stable door after the horse has bolted
  • shut the stable door after the horse has bolted
  • mend (one's) fences