hi the methods you are using to clamp down on your dog, can very easily be done wrong and cause frustration towards your dog which is the opposite of what its meant to do, and end up being confrontational making aggression worse. lots of people in fact most people on here hate those methods, i personally dont hate those methods but do understand the problems they can cause, listen to ClaireandDaisy, i think its time to try some kind understanding training, and check this guy out he makes sense
http://www.dogsey.com/goto.php?url=h...?v=GOW0IKO_zfM
just found out about him yesterday
good luck

oh dear oh dear oh dear. I really do wish people like this could be prosecuted for the damage they do.
Your dog is not `protecting` anyone - except maybe himself. You are not a pack leader. You are not even a dog.

OK rant over

first (to get the AI mellor tosh out of the way) have a read of this : http://k9domain.org/alpha_theory.aspx

Next read a modern book on dog behaviour that is actually based on science and experience, not quasi-new age mumbo jumbo - I recommend The Culture Clash by Jean Donaldson.

If you can, find an APDT or APDBC qualified trainer to help you (The APDT website has lists).

In the meantime - try to be objective about your dog`s behaviour. Muzzle him, and keep him on a line round other dogs. Work on his basic training. Don`t allow him to wander about on walks, keep him actively engaged with you.
Please try to understand that most aggression is caused by fear. Rather than seeing this litter as aggressive, perhaps you could look and see if these are timid or poorly socialised dogs? Then I think his behaviour will make sense.
After castration the hormone testosterone starts to dip - this can take up to 6 months. As a result a fearful dog will become more timid.
This is, however, not the end of the world, as there is much you can do to give your dog confidence and help him learn manners round other dogs. But obviously, it will be easier with professional help.
For now, take the danger out of the situation by working on your basics - recall, heelwork, responding to you and playing with you. This will help you feel more in control, and will take the pressure off him.
And please let us know how it goes.

eta the lady who told you to use distraction and to walk away from triggers had the right idea. Can you go back to her?