I see the terms “watchdog” and “guard dog” used on the web as if they are interchangeable, but they aren’t. There is a difference between a guard dog and a watchdog – a big one.
Watchdog: A Watchdog, also called an “Alarm Dog”, is a dog that is used to warn their owner that something is not right, typically by barking. A common example of the use of a watchdog is to warn their owner of an intruder or trespasser. Watchdogs tend to bark a lot. A watchdog should not be expected to engage (bite) a threat, or even to hold their ground, their job is simply to “sound the alarm”. A good watchdog can sound the alarm and stay out of danger until “backup” arrives to take action. Watchdogs come in many different sizes and shapes. A large size, courage, and amazing strength are not necessarily requirements for a watchdog.
Guard Dog: A Guard Dog is a dog that is used to guard property or livestock (which includes their family – human, canine, feline, fish, bird…). While guard dogs may “alert” like a watchdog, they are also expected to engage (bite) a threat if needed. Typically a guard dog uses a forceful “display” to drive (scare) a threat away while holding their ground and engaging the threat if the initial display is not enough of a deterrent. A good guard dog should always give a clear warning before moving in for a bite – the display is their first line of defense. Guard dogs typically come in 2 packages: large and thick-coated livestock guardians, and large short-coated bully/mastiff type dogs. With the exception being some of the pinscher (terrier) breeds and some shepherd breeds (like the GSD). Size, strength, tenacity, courage, and a level-headed outlook are import traits of a guard dog.
Throughout history the watchdog has been deployed alongside the larger guard dog. The watchdog would act as the alarm while the guardian would come in to take action. Examples of this type of arrangement can be found from Italy, where the Volpino Italiano worked alongside the Cane Corso and Neapolitan Mastiff, from Tibet where the Lhasa Apso and Tibetan Spaniel worked alongside their large guardian counterparts, the Tibetan Mastiff.
Unlike some Protection and Service Dogs, who sometimes require 100s of hours of training (think “Police Dog” or “Military Dog”), watchdogs and guard dogs do not typically need any training for their job, they perform these roles instinctively and autonomously. Actually, it’s my experience that you spend more time training guardians when NOT to guard than when to guard. Like a guard dog, the best Personal Protection Dogs (PPDs) will have a natural protective instinct too, but with the drive to follow-through. Since PPDs are often deployed in public situation (not private property, like a guard dog) the PPD requires a lot of specialized training to ensure the public’s safety.
There is also another type of security dog: the Personal Protection Dog (PPD). These dogs also work on instinct, but are typically always with their human. They’re rarely expected to sit back at home and guard the property while their owner is gone – instead they would be with their owner as their primary job is to protect their owner from “bad guys”. These dogs require a lot of training in the area of obedience and control, and probably pose the highest liability to the owner. A typical should be expected to engage and eliminate threats – without guidance from their handler. These dogs “read” the situation, and act on instinct to protect their human. These dogs require a lot of socialization so they can best “read” their environment and different scenarios.