There comes a time when enough is enough, and the posturing of the lunatic regime of N. Korea (complete with kidnappings of foreign nationals on foreign soil, planned starvation of their own nationals, and random acts of military aggression against other nations) has long since crossed that line.
The question shifts to how best to respond to a heavily armed regime led by barbarians and madmen. Diplomacy has obviously failed in the face of repeated duplicity on the part of the N. Korean regime.
Thus, I offer a modest proposal (unlikely as it is to even be heard of, let alone endorsed by our own executive branch gaggle of idiots and miscreants) as a preliminary response to this latest shelling, with "doing it on the cheap" a clear factor in my thinking, both in terms of blood and money.
Send food, information, guns, and money - distributed randomly by unmarked low-cost, low-radar signature, and low-flying unguided or primitively guided drones. Each drone, under this proposal, should cost less than $5,000 fully loaded with 80lbs of rice, 20lbs of dried meat, 10 FP45 Liberator pistol kits (current production), a dozen wire garrotes, a wind-up radio, and 10,000,000 N. Korean won (the NK currency, in this instance printed by vendor of choice). Every Nth such drone, swap out 10lbs of meat for 9lbs of c4, a detonator, and instructions/suggestions for use.
Ideally, these little CARE packages would be sent north from S. Korea numbered in the hundreds...making life more festive for the barbarians and madmen ruling that rogue nation state.
80lbs of rice and 20lbs of dried meat landing in the N. Korean countryside in the depths of winter is not an inconsiderable bounty - one which could tend to lead to questions about just how hostile the provider of such benefits truly be to the recipient. And serve as bait, to those as would otherwise be wary of life's little surprises - after all, that could make the difference for a family in the depths of a N. Korean winter.
Pistols and garrotes (and the occasional c4 fun kit) are a bit less friendly, but certainly likely - in the hands of a hungry/angry populace - to add a bit of festive chaos to a regime for whom order and control hold a near fetish-like devotion. Not to mention it's harder to control a populace that can fight back, all of a sudden. Toss in a guide on body disposal, and stand well back.
The currency? A multi-purpose package - destabilizing a nations currency is never a nice thing to do, and starving peasants almost *never* see it that way. It's time to go buy some food, a shovel, or bribe ones way outta the country!! But there's a second, more subtle, reason - payback is a bitch.
For decades, N. Korea has been busy about counterfeiting U.S. currency with the dual goals of de-stabilizing our economy and funding their weapons development and production programs. We may not be able to fund anything buy dropping millions of fake N. Korean won into the country - but we sure can de-stabilize what is laughingly called their economy. With the eager assistance of their impoverished populace, who are unlikely to see the downside of gifts of large sums of unmarked cash in small bills.
The drones? For nostalgia, one could go lighter than air...but a more likely approach would be to construct the primitive drones using a lawnmower engine or two, wood and fabric construction, and absolutely primitive guidance (perhaps simply aiming it north and varying "range to crash" by modifying fuel load?).
Obviously, the goal is two-fold - low radar/visual signature and minimal expense. To blow something out of the sky, you must first see (acquire) it either visually or using some other means (radar, etc). Acoustic acquisition really isn't all that effective at this point, to the best of my knowledge. Fiberglass, bamboo, wood, and fabric all create a lower radar profile than metallic surfaces - and are typically cheaper to work. A lawnmower engine is cheap, and a light wood or fiberglass prop is similarly fairly low-profile. If one wants to go ground following, toss in passive GPS and minimal controls and guidance designed for low emissions.
Send them north unmarked, or marked as N. Korean Gov't emergency relief craft...and stand well back.
Not the answer, but certainly a way to disorganize the hostiles while we formulate such an answer.
Of course, this would require an administration both opposed to N. Korean aggression and willing to do something about it.