guard dog

A guard dog or watchdog (not to be confused with an attack dog) is a dog used to watch for and guard people or property against unwanted or unexpected human or animal intruders. The dog is discerning so that it does not annoy or attack the resident humans of the house. History The use of dogs as guardians is well known since ancient times. The Romans used to put mosaics (Cave canem mosaics) at the entrance of the houses to warn visitors and intruders of the presence of dangerous dogs at the property.