lol saitama the troll strikes hard xD

You are forgetting something very important. The deathnote does not kill by itself, it needs a way (hearth attack, fall of building, being run over by a car, etc.), and none of those ways can kill Saitama. If I remember right, if the conditions ot kill someone aren't met within a time margin, it just cancels.
The only way would be to specifically state that Saitama is killed by somehting more powerful than him, but for that to work said thing should exist.