close, lock, etc. the barn door after the horse has escaped

idiomPart ofbarn

close, lock, etc. the barn door after the horse has escaped — idiom

1. This means trying to fix a problem after the damage has already happened.

1.idiom
Definition

This means trying to fix a problem after the damage has already happened.

Example

Maya installed antivirus software after her computer crashed, closing the barn door after the horse escaped.

Did Diego really think locking the gate after the dog ran away would help?