I've just spent 5 minute laughing sooooo hard. . . .
A FIRE EXTINGUISHER !!!!
A head collar as Nix suggests will give you more control, if he "goes" for another dog.
Also consider a muzzle, so even if he does get close, he can't inflict any damage.
Is there anywhere you can let them all off lead to socialise.
A secure back garden ??
One of the problems (we have this with Echo) is that when a dog is ON lead
and is approached by another dog, the fight or flight reflex kicks in.
However because they are attached to a lead and so CAN'T RUN from the approaching dog
they see their only recourse is to FIGHT. And so they get aggressive.
The same dog when encountering dogs OFF lead (in a secure area) will run and play and be more social.
Because he/she has the choice of approaching or being able to back away.
I hope this helps to put things into perspective