I understand your frustration. My Duke does a similar thing. He's never tried to bite anyone, but some people he is completely fine with, and others he's barking, snarling and growling like Cujo..lol
I do think think some of it is a territorial/protective thing, as he will do it more so when he's with me. However, he does it at home when people come over too. He also crouches (like at cat) and pouches on my 65lb lab/chow every time she comes in from going potty. He snarls and jumps on her head to bite her ears.
I correct him for it, but we have been unable to stop it.
Good luck, I will be interested to see what suggestions others make. They think they are big dogs in disguise.
