The map at the article Camilla linked was illustrative: It purports to show sites of 150 "incidents" between North and South Korea since the "armistice" "ended" the conflict. A total of FOUR occurred outside South Koreas land borders (all but one of those in open sea). That said, I'm still not convinced a military strike is the next logical step, but we should break off diplomatic relations until/unless North Korea demontrates some significant and tangible concessions. Simply crawling to them for another agreement they can violate with impunity while they prepare for a war of their own choosing would be stupid. How many people must they kill before the US and her allies are no longer the aggressor? We're past that point, IMHO, and should clearly say the next attack will be treated as the act of war it is, will initiate a war we will conclude on our terms.

Of course, that does mean some pretty awful things, things like North Korea shelling South Korea (because, remember, as long as we sit mutely taking this crap North Korea won't unleash an artillery barrage on South Korean civil--oh, wait, that's a proven load of horsecrap, isn't it? ) and the US confronting China, but it should be clear to any objective observer by now that that day is coming whatever we do.