I've mentioned above the possibility of using eLORAN as an alternative to GPS, because of its inherent resistance to jamming.
It seems that South Korea is already deploying eLORAN as a defence against GPS spoofing by North Korea. This of course will not assist civil aircraft visiting the area since they will not be suitably equipped to receive it. But other countries are working on the necessary ground systems to deploy eLORAN, and airlines should be looking now at suitable upgrades to their navigation equipment.
Meanwhile .. back in the Good 'ol NK ....