use a penetrating oil (like wd-40). Try to tightening it a bit before loosening it, if it moves, try to back it out. Tapping/hitting the head as you apply torque to the fastener will help a bit. If you round out the hex, get a good pair of vice grips and grip the outside of the fastener. You will cut big groves in the head but it is already rounded out and shot. And lastly, drill it out. if it is a blind hole, buy a left handed drill bit that is smaller then the minor dia of the fastener threads. If you are lucky, the left handed drill will back it out of the hole and your existing threads on the ice tool will be fine. This is easier said then done esp if you do not have a drill press or mill.