watch-dog

watch-dog
n
(a) dog that is kept to guard property, esp a house 看门狗.
(b) (fig 比喻) person, group, etc that acts as a guardian of people's rights, etc （监护人们权利等的）监察人, 监察组织
    [attrib 作定语]
a watch-dog committee 监察委员会.

牛津英汉双解词典