watchdog

A dog trained to guard people or property.

One who serves as a guardian or protector against waste, loss, or illegal practices.

A dog kept to watch or guard premises and property.

A dog kept to watch and guard premises or property, and to give notice of the approach of intruders.

a guard dog

a person or organization that monitors and publicizes the behavior of others (individuals, corporations, governments) to discover undesirable activity.

To perform a function analogous to a watchdog.

To guard and warn.

a guardian or defender against theft or illegal practices or waste

a dog trained to guard property