Before you hire off-duty police for private security, shop around a little. In the past, some concert promoters have hired the Hells Angels for security at a considerable discount.
Because it worked out so well at Altamong?
I'm not saying they're angels, but I've never had a problem with The Angels as security: everybody knows 'don't mess', and things are good.
I've seen a few mild beatings, but considerably less that the same fone by 'regular' bouncers down town (though they're getting better....must be all the cameras).