guard duty

a military assignment involving watching over or protecting a person or place or supervising prisoners.

Origin of guard duty

First recorded in 1890–95

The guard-duty was every third day; we had to stand two hours, and off four, rain or shine.

The Empty Sleeve |Henry H. Meacham
One pay-day, when the half of our company was on guard-duty, he for once came back too late.

In the Foreign Legion |Erwin Rosen
Read up the manual of guard-duty for all you're worth before guard-mount to-morrow morning.

Uncle Sam's Boys in the Ranks |H. Irving Hancock
But it happened that Ildiger and his men were keeping guard at that time; for all were assigned by turns to guard-duty.

Procopius |Procopius

The Federal soldier seated on the sand-bags is on guard-duty to prevent camp-followers from looting the vacant fort.

The Civil War Through the Camera |Henry W. (Henry William) Elson