stand guard
stand watch
keep guard ,
stand sentinel

Keep your guard up, and come back to me in one piece.

Here they stand for Germany and keep guard over our people.

So they were keeping a guard of their own on him.

He was allowed to keep a personal guard of six hundred men.

It would change hands again unless the men kept guard.

Howard is to stay near the car to keep guard.

They always kept a guard on duty, just in case.

The man was gone and the girl had now settled herself down on the floor before the door to keep a guard over her.

One thing was certain, he'd have to work harder to keep his guard up against her from now on.