stand guard
stand watch
keep guard ,
stand sentinel

One hundred fifty fire trucks stood sentinel on the narrow winding streets.

Others are shaped like huge eggbeaters standing sentinel over the valley below.

On many rooftops, men stood sentinel with weapons in their hands.

A huge oak stood sentinel over the empty grave.

A solitary cottonwood that had already shed its leaves stood sentinel at one end.

Two of us would stand sentinel while the other two were swimming.

I take the significance of this to be that the one Rider who had stood sentinel under the trees went to fetch the other two.

Or from the cypress trees that stood sentinel outside the park gates?

Always, she kept trees between herself and the meadow over which the hunting stand stood sentinel.

On the hill overlooking the harbor entrance, a huge French fort stood sentinel.