In what I think is the right posture for them, South Korea is flexing their muscles enough that the North should think twice about repeating any of their recent aggressions: New South Korea exercises to test border tension.

I think this is probably the only reasonable response.  Clearly doing nothing was just providing an incentive for the North to keep attacking, and the South’s population got sick of doing nothing.  But, the South can’t really instigate because everyone’s afraid that’d lead to all-out war, and even though the North would be easily beaten, the initial artillery shelling would deal quite a bit of damage.