At the beginning of your upkeep, put a fuse counter on each creature with a fuse counter on it.
Whenever a creature has four or more fuse counters on it, remove all fuse counters from it and destroy it. That creature deals 4 damage to its controller.
10/4/2004 If the creature regenerates, the fuse counters are still removed and the four damage is still dealt.
10/4/2004 If there are two Bomb Squads on the battlefield when a creature ends up with 4 or more fuse counters, both Bomb Squad abilities will trigger causing 4 damage each even though the first to resolve will destroy the creature.