on guard

The sentry is on guard.

那哨兵在担任警。

"It's raining hard enough to put out the very devil's fire. And the bobbies will be along instanter. There's a soldier on guard yonder. We shall get nabbed here."

“下得连鬼火也熄灭了。并且警察就要了。那边有个兵在站岗。我们会在此地住。”