My players have a habit of preparing for the worst. Knowing the planned escape route, the chopper, my group's resident rigger/mechanic sprung for an LMG and associated mount. I told him he he could get it to the roof, he could bring it along. It certainly wasn't enough to down Drexel, but the hail of EX-ex was enough to dissuade him. It didn't keep him away forever, but any job you can walk away from is a good one