Here are a couple of suggestions for you.

1) obediece training with a good
behavior/obiedence trainer.
2) Try a collar called the Gentle leader
head collar. Your dog might not
take to it, but if he does,
it works like a miracle.
I have a large dog dominant pooch
that can't pull me when he is wearing his.
They have a web site with all
the information. I bought mine
through E-bay auction at
1/2 the cost, but I already new how
to use it.
It is very important that
you put in on your dog properly.
If your dog is real strong, as a
safe guard you can also attach the
leash to a choke chain for back up.
You do not use the gentle leader
like a choke. You simply guide your dog
just like you would a horse wearing a halter.
The dog goes where his nose does.

Good luck. : )