Have you read the books by the Monks of New Skete? They raise German Shepherds and we've always loosely based our training of them on their books.
I'd say it's important to make sure he understands he's at the bottom of your family pack. Please believe me that I don't say this lightly, but if you can't break him of his aggression, you've got to put him down. I'm terribly sorry.
I LOVE that book by the monks of New Skete, about raising and training their shepherds. Outstanding!
I'll say I have always been very firm with him when he has needed it. But, he doesn't blink.
My husband on the other hand finds it hard to reprimand. But, does try because he knows this is serious.