The guard was on duty all night. ✬

Be on your guard against pickpockets. ✬

You'd better stay on your guard. ✬

Tom has been a prison guard for ten years. ✬

Tom is a security guard at the airport. ✬

Tom was accused of falling asleep on guard duty. ✬

Not knowing what to expect, Tom was caught off guard. ✬

Tom couldn't get past the guard. ✬

The security guard told Tom that he couldn't take pictures in this area. ✬

Don't let your guard down. ✬