Thomas Dai & Tim Gavrich have encapsulated my thoughts on this fascinating topic. Although the moniker is not military, is there a more strategically appropriate defensive position than a volcano? My favorite is #2 at Eagle Springs in Wisconsin. Your only chance is a properly judged mortar shot of the appropriate trajectory and weight. Anything less than perfect bounces harmlessly away from the fortress that is the green, and recovery is up a slope so steep you're firing over the head of the defender (i.e. you can't see the flag).
And what defender wouldn't want a volcano in their rear? If the ramparts are breached, it can spew hot lava over the attackers.