Right now our interest is on guard dog. Just now while chatting with Wan there's a question whether a guard dog should be non-friendly or always aggressive.
I believe guard dogs should be socialized with dogs and humans and only attack on command or at specific situation. Here I found a video on how K9-1 do their protection dog training.
As you can see in this video, the person who was attacked by the dog could pet the dog after that because owner ask him to be 'easy'.
