What Brigitte was communicating, was that this was a dog who would routinely classify things, all his life, as his and not-his. It was a sign of a very powerful drive of territoriality and dominance. When your puppy is three months old, he is ready for puppy training, also known as puppy kindergarten. If you have the option, and there is a place near you that offers the service, by all means go. Most dog owners at this stage know their little dogs pretty well, and many of the shortcomings of their personalities have come into view.
Puppy training is the first time owners present their dogs to the world.
Owners are not dogpeople at this point. They are an odd, insectlike, six-legged race, with the two species constantly jostling and tripping the other. This hatred of others is both a badge of pride and a token of something darker, the fear that you have made a terrible mistake you are going to have to live with for the next fifteen years. This is the danger stage in dog ownership, when many people conclude that the relationship is not working out. The puppy may still be pooping all over the house, destroying valuables with its teeth, and biting people.