With a few exceptions, any breed, large or small, can be trained as a watchdog dog, even a Yorkie or a Pekingese. As they mature, dogs naturally develop the ability to bark moderately to signal the arrival of a visitor. The ideal watchdog does not bark too loudly or insistently and, generally speaking, does not bite or attack. Puppies usually start barking between the ages of four and six months. If the owner fails to immediately correct the problem or encourages the barking, the dog will bark too much and guard his environment more aggressively. Norhtern breeds in general are not especially good watchdogs (except Eskies), but they are vocal and they howl.