Dog-Dog Socialization also deteriorates during adolescence, often at an alarming rate, especially for very small and very large dogs. First, teaching a dog to get along with every other dog is difficult. Groups of wild canids — wolves, coyotes, jackals, etc. — seldom welcome strangers into their midst, but that's exactly what we expect of Canis familiaris. Second, it is unrealistic to expect a dog to be best friends with every dog. Much like people, dogs have special friends, casual acquaintances, and individuals they don't particularly like. Third, it is quite natural for dogs (especially males) to squabble. In fact, it is a rare male dog that has never been involved in some physical altercation. Everything was fine with young pups playing in class and in parks, but with adolescent dogs, the scraps, the arguments, and even the play-fighting seem all too real.
A dog's first adolescent fight often marks the beginning of the end of his socialization with other dogs. Again, this is especially true for very small and very large dogs. Owners of small dogs are understandably concerned about their dog's safety and may be disinclined to allow their dogs to run with the big dogs. Here is where socialization starts downhill and the small dog becomes increasingly snappy and scrappy. Similarly, owners of large dogs (especially the working breeds) are understandably concerned that their dogs might hurt smaller dogs. Here too socialization goes downhill and the big dog becomes increasingly snappy and scrappy. Now we're in vicious circle: the less the dog is socialized, the more likely he is to fight and thus be less socialized.