My 9 month old Wheaten Terrier Cross (I think with a Glen of Imaal) got into a fight today with another entire male. My dog was bit on the nose and blood drawn. It was unnerving for me and the other owner (and the dogs probably).  Took him to the park on a lead later in the evening as I didn't want him becoming afraid of other dogs - but another entire male growled at him.  The thing I've noticed is that my dog doesn't seem to heed a warning growl and back off - he keeps going back.  He doesn't seem to start the fight - but once provoked won't then back down.
I don't want to be a scared dog owner so what is the best thing to do do you think?
Keep him on a lead? (if so what happens if an entire male comes charging towrds us!!) Get him castrated?
Any advice would be very welcome.

Wheatens are described as friendly, and whilst shouldnt start a fight, wont back off, so I'm afraid it is  his natural make-up and I doubt castration would make a huge difference. Training is the answer - to get him to back off on command from you.

He is a terrier!

I have a bedlington x here, he is a lurcher, and generally is a happy, easy going kinda dog. But true to his working terrier background, whilst he wont start anything, he'll have a damn good go at finishing it, and he doesnt care WHO it is thats fighting, he wants a piece of the action!

Training training and more training.

Train a leave or 'out' command, starting with stuff thats easy for him to be distracted from and working up slowly to stuff thats quite exciting.

Id go for clicker training and i would also have a REALLY good think about the dogs way of thinking, really get to know your dog and do lots of training and games that will help improve the bond between you.
Terriers are bred to think for themselves, so you need to earn his respect and trust so that he will listen to you.

Em