I'm with Boo on this -
dogs are pack animals, and a natural leader will always emerge. The problem is, it's the nature of the pack memers to have a tilt at the leadership now and again, and as you have discovered, if the odds are in favour of one by virtue of breed and natural strength and agression, he will fight to assert his position, and make sure the challenge is dealt with. in the case of a dog like a staffie, this can easily mean maiming or killing the interloper.
So, you have to consider the safety of your other dogs, because this will happen again, it's pack nature, and you will never be able to prevent it.
You must also consider the children who walk your dogs. Dogs consider humans in regular close proximity as members of the pack, and in the case of children, the dog may regard one of them as a pretender to his leadership - and the results wil be the same.
You have to make a decision. Now.