Let one’s guard down and drop one’s guard

Let one’s guard down and drop one’s guard are two variations of an idiom that may not be as old as you think. An idiom is a commonly used word, group of words, or phrase that has a figurative meaning that is not easily deduced from its literal definition. Often using descriptive imagery or metaphors, […]
from Grammarist
https://grammarist.com/idioms/let-ones-guard-down-and-drop-ones-guard/