It's not a fail-- you use your tower shield (on which the runes are written) as cover from the Explosive Runes effect. You write the runes in very large font so you can read them from very far away- so whoever is within 20 feet or so ("close enough to read them") takes 6d6 force damage with no saving throw, and anyone 10 feet in front of the fighter takes 6d6 force damage with a reflex save for half. This is harder to do on armor and helmets, so we used Symbols of Pain, Fear, etc instead. It's cheesy, but it works. We only did that one time while wading into an enemy army to eliminate one specific noble.
AMF and MDJ are extremely annoying, especially when MDJ permanently disables your magic items. It's fun to strip the BBEG's buffs, though.