guard · n
catch sb off guard
C2 to surprise someone by doing something when they are not ready to deal with it
Dictionary examples:
The journalist caught him off guard and he admitted to lying. (37.2)
be on (your) guard
C2 to be ready to deal with something difficult that might happen
Dictionary examples:
Companies were warned to be on their guard for suspicious packages. (46.1)
let your guard down
C2 to relax when you should be careful or ready to deal with something
Dictionary examples:
He's worried that if he lets his guard down someone may take advantage of him. (50.5)
guard
B1 someone whose job is to protect a person, place or thing from danger or attack, or to prevent a person such as a criminal from escaping
Dictionary examples:
The mall guard chased a thief but got distracted by a sale. (0.0)
The library guard's main duty was to protect books from noisy readers. (0.0)
The zoo guard's job was easy until the penguins decided to escape. (0.0)
prison guards (30.6)
a security guard (37.2)
The frontier is patrolled by border guards. (75.0)