Has it really come to this? In America?
If I were a state legislator, trying to allay a clamoring constituency concerned about creeping sharia, I'd pass a resolution. Not a law, a resolution. It would be sufficient for purposes of re-asserting the primacy of American law over sharia law, without having to generate a lot of expensive, possible ineffective, and most probably embarrassing, enforcement.
The language of the resolution could simply state that the laws enacted by the democratically-elected government of (your state here) are the law of the land, and any laws passed by any religious body have no standing or effect against them. There are doubtless problems with that wording, but then I'm no lawyer. But it could be worded to make it clear that polygamy, wife-beating, honor-killing, keeping household slaves, funding or otherwise supporting terrorist groups, or letting little boys whip themselves with razors during Ashura are all right out of the question in our land and under our laws.
And, to come clean, I should say that I believe these matters are due to be clarified, after decades of multiculturalism. Some years ago the Canadian province of Ontario toyed with the idea of permitting sharia law to be practiced there. They dropped the idea, in part because of the protests of otherwise liberal Muslim women activists like Alia Hogben. She knew what would be in store for Muslim women if fundamentalist Muslim men were given the whip hand. The Land Of The Free should do no less.