leave (one's) guard down(redirected from left his guard down)
leave (one's) guard down
To become less guarded or vigilant; to stop being cautious about potential trouble or danger. We'll wait long enough for them to leave their guard down before we launch our invasion. There will always be people in this business looking to exploit you, so you can never leave your guard down.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.