You didn't look at the Supreme Court's decision closely enough

Yes, I did. I'm looking at the one before, where they had to move the buoys because the river is an international waterway. The navigable part of the river includes up to the bank, and the river raises and lowers. This raising and lowering causes a zone on the bank that would be part of an area where they can't put razor wire, if it follows the normal law and IIRC. If it were me and the razor wire was placed 10 feet back form the high water mark, I would have no problem with it unless in practice that was too hazardous for some unforeseen reason.

If you place the razor wire at the high water mark, you create a foreseeable hazard for the illegal/asylee. If you go to the edge at the low ebb, it's a hazard. If you extend into the water at low ebb, you are an inhuman bastard just killing people.