To completely seal off Japan from North Korean amphetamines, terorists/bombers, espionage agents, kidnappers, and counterfeit cash, they would literally have to abolish the JAPANESE YAKUZA, (organized crime), and everyone knows as long as there is such a thing as a local, prefectural or national politician (particularly Liberal Democratic Party) or police chief in Japan, this will NEVER HAPPEN.
They will find a way around any roadblock to keep getting these things into Japan and getting pachinko money out to enrich the uranium and improve the missile guidance programs.
[Say, enjoy a few maguros, sabas, kampachis and ikas in Nippon for me, sushiman.]