True, but we're several developments, I think, from mining the harbors.
We have international support at present, grudging perhaps, to inspect all cargo ships for contraband. Sinking vessels simply for entering or leaving NK ports isn't in that mandate.
I agree that talking is all that is going on. It probably will be the only thing which happens. NK will go down in 12-18 months if we keep the economic pressure on. Faster would require either military action of some sort or closure of the Chinese border.