If God is material - and the Bible often speaks of him as such - then nuclear weapons should be enough; probably overkill in fact. If he’s something more exotic then black holes should work; making or grabbing one is a tiny bit beyond what we can do yet though. Of course, both methods require he make an appearance.
Wake up Godzilla, and send him against God; Godzilla can handle iron chariots just fine so we know who’d win, right? 
An idea from the novel The Jehovah Contract that I mentioned in the other thread, in response to Ranchoth’s comment.
If gods are defined or powered by belief, convince people that God can die. They had a a whole “Godkiller” ad campaign, complete with “Godkiller” T-shirts with the logo and a slogan (this was written before 2000) “In the first day of the year 2000, God will die.”