I'm not sure, and neither is the guy who's writing this book! However, he has given some thought to the matter and written a very interesting article about how such a thing might or might not work:
That's wonderful. He argues that libertarian societies will evolve from consumer free choice of law enforcement, toward a situation where all providers collude to form a single set of laws that is convenient for them to provide.
Oligopoly is apparently the natural order of things.
Oligopoly is apparently the natural order of things.