let guard down

let (one's) guard down

To become less guarded or vigilant; to stop being cautious about potential trouble or danger. Also worded as "let down (one's) guard." We'll wait long enough for them to let their guard down before we launch our invasion. There will always be people in this business looking to exploit you, so you can never let your guard down.
See also: down, guard, let

let one's guard down

Fig. to stop guarding oneself against trouble; to relax one's vigilance. He never lets his guard down because he trusts no one.
See also: down, guard, let
References in periodicals archive ?
In the light welterweight category, Brazilian Myke was defensive from the beginning and attacked Kumar who let guard down.