No additional law is needed. The laws of the state and country are in effect. shitaria laws contradict those laws, and are therefore invalid.
Anyone who comes here promoting shitaria is not eligible to be a citizen or to stay, since shitaria promotes the violent overthrow of our government.
You are exactly right. It becomes a double speak conundrum but unnecessary as the constitution disallows Sharia while not specifically addressing Islam or Sharia Law.