Pretty cool you live so close to Old Trafford. I'm kind of jealous. However I don't know much of a problem military personnel played into football violence. Sure there are those rotten apples but by and large I don't think it military. This is not discount what you witness, but I would think this the exception and not the rule.
In the seventies and eighties the army was at it's lowest figures since before the Second World War, it was severely stretched and had only half the numbers it needed in BAOR so the idea that thousands of soldiers were released on leave to go to a football match is ridiculous in the extreme. The only violence recorded in Amsterdam was in the UEFA cup final in 1974, when Spurs fans destroyed part of Feynoord's stadium, they didn't destroy Amsterdam. the police violence that day was also supposed to be pretty shocking because it was the first time Dutch police had faced this and they reacted strongly.
This is a good article which explains much about the football firms, how you form a defence against this I don't know, other than not to be in their way perhaps or not in a rival firm.
The hooligan problem and football violence that just won't go away | Jamie Jackson