Quis custodiet ipsos custodes?

Question:

Quis custodiet ipsos custodes?

Please, intelligent answers only. =)

Best Answer - Chosen by Asker: Other watchmen. If you're really clever, you go for a "separation of powers" principle, with "checks and balances", so that each set of watchers is watching another set of watchers, with little opportunity for quid pro quo or perverse incentives.