Yeah... people tend to forget that modern artillery is actually in the 10-20 mile range to begin with. But that is really no different than "begin the invasion". It isn't like South Korea (and North Korea) aren't watching the other side 24/7.

It is just that people usually use nukes as the exigent circumstances in a time like this. And I am going to specifically not speculate as to whether a nuclear bomb could be launched from behind the DMZ.