8 month old super alpha and increasingly aggressive, to die

Question
Please, please help me decide the best thing to do. We got Zeus at 8-10 weeks old from the pound and he was in very bad shape. He is a GSD mix and just gorgeous. He was also very sweet in the beginning but showed his alpha personality from the start. Over the last 9-12 weeks he has gotten terrifyingly viscious. I don't know if that's the right word but he is growling and biting us. Except for my husband. Steve is the only person Zeus sees as his boss. then the 14 year old boy, then me, the mother and lastly our 11 year old boy. It appears that the pup really would like to have Dylan for lunch and me for dinner. I am 48 and have had dogs my whole life. I have rudimentary training skills, enough to usually get by but not with this guy.

He was lying near my feet recently and I reached over with my foot to rub him. He nearly took off my toe. When Steve is gone Zeus feels he is in charge of the house. I try to work with him but not when Steve is gone. I've never been afraid of my own dog before and I am terrified that he will do horrendous damage the my son, the 11 year old.

We all love him, he is so smart, maybe the smartest dog I've ever seen. But increasingly he acts as if he would be happy if we would just leave him alone.

Steve says he must be put down....... but I hope that you can shed some light on this and help to fix him. If he can be fixed. Can he?

Please let me know your thoughts before he does irreparable damage. Or before he is put down unnecessarily if that is the case.

By the way, he is rarely at home alone. Maybe 3 times in his whole life.

Thank you so much for your time.

Answer
Having him neutered if not already and a good obedience program concentrating on you as top dog should help.  So should imposing these rules on him, http://www.dogbreedinfo.com./topdogrules.htm  

However, the above may not be near enough.  A large, aggressive dog could hurt somebody and it will only get worse as he matures.  Like most medical problems, this may not be a good problem to try to handle over the net.  I don't know how to fix the problem, and don't trust anybody else on the net.  I also have more confidence in the average vet than many private dog trainers and behaviorists.  some of them will take your money and rather than admit they can't fix the problem, say the solution is a 3 hour walk every day.  

You might find a rescue organization that would take him, or even help you to retrain him.  Rescues take dogs that lost their home and put them into a foster home to be retrained as necessary and placed in the right home for them.   You may find a rescue near you starting at http://www.akc.org/breeds/rescue.cfm