Isn't he actually a specialist in *failing* to destroy an indestructible being, though? I mean, Superman's still around, the one time he 'died' it wasn't Luthor, and he's got some fairly well-known (if not initially obvious) weaknesses.
Given that Swampy when between bodies is essentially a spiritual being able to make journeys to the afterlife, this does make you wonder if an ordinary communications scrambler could be modified to retune, say, Deadman, the same way. Does Luthor have soul-scrambling technology?