watch-dog

例句：

1. 1. The watchdog patrols the neighborhood at night to keep the peace.
   夜巡犬巡逻着这个社区，以维护和平。
2. 2. The watchdog was a loyal guardian of the village.
   看门狗是这个村庄忠诚的守护者。
3. 3. The watchdog was called upon to catch the thief in the act.
   看门狗被叫来当场抓住小偷。