Seoul needs creativity in its defense strategies. That is, it has to think outside the box and come up with ways to defeat the northern strategy, as well as to hit them in their most vulnerable areas.
To start with, North Korea has 7 major dams, 4 of which are used to generate hydroelectric power. If this and other power sources are neutralized, winter will be devastating to North Korea.
North Korea also gets major resupply from China by rail. This means track and bridge vulnerabilities.
Just some examples.