States have the power to erect their own wall on their southern borders to control the flow of immigrants entering their respective States and to establish border crossings. But the states don’t want to pay for it. Still, I would apply as a state for federal funding for the wall. Each border state affected by immigration applies. Make the federal government say no. They won’t.
Of course if the federal government funds it, they’ll want to control it. Let them.
It might be a good idea for the states to confer with each other on design – for aesthetic purposes. You can have a different design for each state, but they must flow with each other. No albatrosses. And no easy marks.
Amendment X to the Constitution of the United States
Powers retained by the states and the people
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
If the States say no and the Federal government says no, then the people can demand security for their individual states. WE THE PEOPLE.