We know that dogs have descended from wolves that have a significant instinct to defend territory for it’s mating and food resources. In dog’s, territorial aggression often manifests itself as aggression towards humans as we are the most likely beings to broach on what a dog thinks of its own territory.
Often we unintentional reinforced territorial aggression in dogs. Take for example the behaviour of the postman and milkman who enter your premises. Your dog barks loudly, and then the person leaves (after they have done their delivery). Of course your dog does not understand this; it thinks that aggressive and loud barking has successfully chased the person away. An important preventative measure to take to avoid this is to ensure your dog is introduced to visitors and delivery people at an early age.
One good suggestion by Gwen Bailey (author of a number of renowned dog training books) is to install a small weatherproof container near your garden gate. Leave treats in this container and ask your postman to give these to your dog when they enter your property. They can also drop a few of these treats through the letter box when they leave the post. Both of these measures help make a positive and rewarding experience out of visitors entering our premises.
For further hints and tips on preventing barking at visitors, read our training article Train your dog to be QUIET. The article Why is my dog aggressive to people also looks at the different reason for aggression.