let one's guard down
let down one's guard
lower one's guard , także: let guard down

I let down my guard thinking you were safe here.

But was it important enough for them to let their guard down?

I let down my guard, but only for a moment.

Nor does he let down his guard for a moment.

I think they've both had the chance to let their guard down with one another.

You can't ever let down your guard in a place like this.

The women tried to make the men set over them let down their guard.

But at the same time, you can't let down your guard.

"Why have you now at last let down your guard?"