Carrying a DEMP blaster in your belt might not be a bad idea though. Criminals will have them - Directional ElectroMagnetic Pulse pumps that can sense the operating frequency of malignant AI and zap it's circuits with a resonant pulse!!

But coming back to your post - maybe benevolently designed vigilante AI constantly scanning for bad or suspicious behavior of AI setups and their potential creators all over could be a good starter for keeping the playing field clean.