quis custodiet ipsos custodes?

Who will guard the guards themselves?

Notes

Commonly associated with Plato who in the Republic poses this question; and from Juvenal's On Women, referring to the practice of having eunuchs guard women and beginning with the word sed ("but"). Usually translated less literally, as "Who watches the watchmen?" This translation is a common epigraph, such as of the Tower Commission and Alan Moore's Watchmen comic book series.