I read a book that was about the DMZ. I will have to go find it but it said something about the casualty rate on the DMZ was all most as bad as Vietnam during the 60's.
Being in an Air Cav unit, we didn't have much to do with the "lowly crunchies", so I never really met any of the infantry who patrolled the "Z". We did hear about firefights a couple times, usually because they resulted in alerts that had us launching aircraft to get them off the airfield. After the first month I stopped worrying about alerts until they started issuing us .38 ammo...
We did have a couple major incidents while I was there. Probably the one that brought us closest to actually shooting was when an MP major got stomped by a half-dozen NK guards at Panmunjon. Fortunately, our MPs got to him in time to save his life, but he was pretty busted up. The 8th Army CO had us parading up and down the Z with 17 lb rockets in the pods of the Cobras (because the warheads could be seen outside the rocket pods), just DARING the NKs to fire on them...
The other major incident was the discovery of three enormous tunnels under the Z. One of them had a narrow-gauge rail down the middle, and all were large enough to march 8 troops abreast through them.