so much great advice. you've all given me a lot of homework. particularly in tracking down some of that reading material. Thank you!!
so far as the law side goes the furthest i'd gotten were roaming garrisons with either detecting devices or mages employed. I would guess that a big city/state that was systematically trying to control magic would be most concerned about suppressing it from 1st through 3rd levels, knowing that more powerful artifacts and users would be a substantially different problem then just civic order.
I've been thinking about the magic in my campaign as a sort of molecular substance that bonds in very particular ways so that it manifests rarely in stone, mineral and in some instances in plant form (through mineral traces). So, i've been wondering if i shouldn't allow for some sort of "kryptonite" too that is sort of an anti-magic substance.
Please keep them coming if you've got any ideas to share.