At the very least, dogs have been providing protection to their human companions ever since the time of Plato and Aristotle.
In most cases, watchdogs will not harm their people, but they will bark or otherwise alert them to what they perceive to be intruders.
According to Gina DiNardo, executive secretary at the American Kennel Club (AKC), guard dogs have a protective
instinct for their family that has been refined over hundreds of years.
This instinct causes them to bite or otherwise defend themselves against dangers.
The most effective guard dog breeds are those that not only exhibit fearlessness but also look the part,
with a size and appearance that is scary, possibly even belonging to one of the various enormous dog breeds.