While law enforcement has some potentially excludable components, for the most part it seems non-excludable: stopping crimes and criminals protects everyone. Exclusion mostly seems possible geographically, and we already effectively do that at the borders of states and countries. On top of that, unlike education, law enforcement does not have a blindingly obvious solution for how to run it privately. (While I understand that solutions exist for how to "privatize" law enforcement, any attempt to privatize the use of force has huge difficulties and dangerous pitfalls.)