That's really naive. But what they SHOULD do is build TWO bunkers, one on top of another. Like bunk-beds. So bunker buster busts a top-bunk bunker, but bottom-bunk bunker be unbusted.
And I know what you're thinking. They'll just make a bunker-bunker-buster. So you just make a bunk-bunk-bed bunker. You've basically got a bunker arms race going. It's bunkers all the way down.