The search function has been broken for some time now.
Private prisons - response to Moore’s film Oct 3 2009
Justice system under anarchy: private security, judges, prisons(?), arbitration etc Feb 24 2010
Anarcho-Capitalist Law and Order Aug 5 2010
How would free market prisons work? Oct 27 2011
Punishment in a libertarian society Sep 27 2012
(Also be sure and check Courts/Law, Security/Defense)
Those were just the ones I found in a quick one-keyword search. I’m sure if you use the Google longer you could probably find more. (You didn’t really think there was a topic we hadn’t discussed here, did you? )
P.S.
In the future, for a quick reference guide on topics, be sure to check the meta-thread.