Thank you for all your help and information. You don't have to worry about me giving up on my dog, I love him too much and I'm as tenacious as he is, so I'll keep trying with him. A few months ago I seriously thought I'd have to get rid of him after he bit my girlfriend twice, but she loves him as much as I do and she is willing to take one for the team once in a while till we get him straightened out. He has been good with her lately.
She's actually the one who got him, she brought him home from work when she saw how he was neglected, but I'm the one who is with him most of the time. He goes to work with me every day, so he's bonded more to me. I really think he gets jealous sometimes when she's close to me, because that's when he's gone after her.
I do think he knows I'm the alpha dog.
He's never been aggressive with me, he follows me everywhere, even if I get up from a chair and walk 5 feet away, he gets up and stays close to me.
He does have a stubborn and independent streak, and if he want's to go somewhere he has selective hearing and doesn't always listen, so I end up running after him and leashing him when I get him. He probably thinks it's a game. I figure any 40lb dog that can chase 4000lb bulls around has to have some attitude.
I try to run around with him every day for a mile or two, even in the winter, but maybe he needs more activity and stimulation than that. We've talked about training classes for him, but I've never had to do that with my dogs before. I suppose it can only help.
I'll try to keep you updated with his progress. Thanks again for everything.