Are they bred to do so or are they conditioned after birth?
Altough I have very little sympathies for such breeds, I'm more with Jazzmoose here. I grew up around dogs, never had anything serious (actually nothing non-serious either), even though one of them was an aggressive as hell small terrier. My parents tought us kids how to behave and how to treat the dog and it all went perfectly well. Growing up I was eventually even able to pat it ... and it was incredible sad to see the tough bastard make up his mind and slowly leave us (he just stopped eating, then drinking ... and it took days, weeks even, he still seemed kinda alright, but eventually there was nothing left to do but call the vet. Much sadder was fifteen years later (about ten years ago) having to call the vet to kill our next family dog, the one I picked ... glad I happened to be there with my mother when that day took place. Some sad cat stories, too, but I told them before, I think (and I'm afraid dog-lovers will bully me outta this thread real quick, though frankly it never got in my head why so many people seem to have to take an either/or choice .... that tough little sucker I just mentioned even lived along a cat for a few months, before she was run over by a car ... that was before my memory kicks in though).
And all the best to your three-legged companion, Dave!