A guard dog or watch dog is a
dog employed to guard
against, or watch for, unwanted or unexpected animals or people.
Both guard dogs and watch dogs bark to alert their owners of an intruder's
presence. The barking is also an attempt at scaring away the intruder. The watch
dogs's function ends here, while a guard dog might be trained to restrain or
attack the intruder. For example,
livestock guardian dogs are often large enough and strong enough to attack
and drive away predators
such as wolves. In cases where
intruders are more likely to be human, guard dogs are sometimes trained simply
to restrain an intruder with his owner's guidance, as in
Schutzhund
training. Occasionally, guard dogs are trained to attack human intruder(s),
though this practice might be locally illegal.