I remember reading a Planetside 1 fanfic a few years ago called The Triumvirate. The way it represented the war was generally more in line with a modern one, so people died a lot less often and respawning was a rare occurrence; after nine or ten respawns, the failure rate rose dramatically to something like 40-50% due to digital copying errors in the DNA. Basically a soldier had a serving life of about eight respawns before it was no longer safe for him to be on the front line.
Another idea would be a simple broad spectrum jammer; if someone does, how does their conciousness get transferred to the new body? If you jam that signal, then the conciousness stays with the corpse and the rebirthed body is uh... empty.
Or headshots. Perhaps headshots destroy the brain before the mind can be transferred properly.
Plenty of ideas floating around for that.