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The Pentagon is moving toward letting AI weapons autonomously decide to kill humans
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
Put it in hardware. Something like a micro explosive on the processor that requires a heartbeat signal to reset a timer. Another good one would not be to allow them to autonomously recharge and require humans to connect them to power.
Both of those would mean that any rogue AI would be eliminated one way or the other within a day