The Greek White Shepherd is a family dog with a very strong guarding instinct. In general, it is a very friendly breed which, driven by its deep instinct of belonging in a herd, gets very attached to its family, making it very protective.
It is desirable for the dog to be a fearless guard when it is alone in its familiar space, but when the owner is present it should recognize the rights given to strangers by him and not to be aggressive. As for the walks outside "home" it should be friendly with other people and animals.
The intruder from outside should see a large, loud and imposing dog barking at a distance from the fence, without fury (eating the fence), and setting boundaries. This is an instinct it has in order to protect itself from the intruder. If the intruder leaves, the dog should continue to guard the area and not chase the intruder.
The guarding it does is instinctive and rational. This means that the animal keeps its distance until it knows if the intruder is friend or foe. The dog must be tough and relentless but at the same time cautious and sensible.