The guardian breeds and dogs in general are not born with a naturally protective gene that develops in strength as the dog matures from puberty.
Many dogs will by nature keep watch and should be trained to discriminate and not bark at everything in the dog’s line of sight and some have a strong territorial instinct which can cause behavioral problems if control slides from the owner to the dogs.
Territorial or possessive behavior over a human, the dog deciding who can come inside and where visitors are allowed to go as protective, is not a dog being protective.
What is in the genetic makeup of a dog is self-protection, to see to its own safety and avoid threatening situations by removing itself from it or waiting for its owner to handle the problem, perhaps barking if it had a nervy temperament. Some dogs may attack out of a sound temperament, a defensive reaction to the dog seeing a threat to its safety, which may also save its owner’s skin.
A dog has to be born with the potential to be trained as a defence dog by someone who knows what they are doing to protect human life in abnormally stressful situations, when mental pressure is piled on the dog’s temperament and it has to be relied on to perform its task.