I’m certainly not a military planner but they would have to have a fully loaded plane to take out every single one of the artillery areas - one plane for each one - and wipe them all out immediately to protect Seoul, and have some ready to take out any areas where artillery fire is coming from that was previously not detected prior to any conflict beginning. That would be quite an undertaking but one that would be necessary. Seoul being so close to the border is a major obstacle.
Need a 21st century equivalent to the St Lo breakout.
This will not be WW II or the Korean Conflict where plane loads of bombs would be needed for each position.
There are missiles that are now either ready or will be shortly that can glide or maneuver right into the openings. Only the long range arty and rockets would have to be destroyed immediately, so lowering the number of targets dramatically.
I thought the number of artillery pieces on the NK border was 10,000. According to this article it is 13,000.
http://www.popularmechanics.com/military/a6212/north-korea-and-flattening-seoul/
The ones I have seen in previous articles are in deep revetments and would be difficult to destroy.