What is an idiom or proverb to point out half-measures? Something like, "You locked the door, but left the window open." Or, "You wrote the check, but forgot to mail it." Those expressions seem easy to understand, but I've heard them rarely or never. Is there a more common expression?

The question was inspired by ineffective quarantines, such as isolating somebody to their room, but letting the family dog go back and forth.

Update: To clarify, I am looking for an idiom or proverb resembling "You did A, but left out B".