If it is a sovereign nation, then I would cut off all federal, state, and city services, including ambulance, police, garbage, sewer, electricity, everything. A fence should be constructed around the area, and people should only be allowed back into the US if they can prove citenship, and it should take as long as possible to be processed back into the US, and all vehicles entering the sovereign nation should have to go through a check point and all be searched, so as it takes as long as possible to cross the “international border” in either direction.
Oh yeah...when people or vehicles are entering the sovereign nation, all products (including clothing), created by corporations should be confiscated.