Forbidding them reentry on what basis that you can legally uphold vis a vi their being a foreign citizen from another country we are friendly with? Controlling interest in any U.S. company... chances are their company is already by accounting principles registered somewhere else internationally, or they might move asset ownership to some sort of family trust, or form shell companies to hold US Stock that you'd never trace.

I think you're underestimating the legal maneuvers these people can afford to find that have got then to where they are.