audio quid ueteres olim moneatis amici,Wikipedia has an interesting entry on the phrase. You should totally read it when you get a chance. It presents the more common translation in English, "Who watches the watchmen?"
"pone seram, cohibe." sed quis custodiet ipsos—
custodes? cauta est et ab illis incipit uxor.
I hear always the admonishment of my friends:
"Bolt her in, constrain her!" But who will guard
the guardians? The wife plans ahead and begins with them!
The magical implications of this question are multifaceted, multi-layered, and as deep as any question we can ask ourselves. While reading Heart Drops of Dharmakaya, I was impressed with the Dzogchen practice of observation during meditation. I'm no Dzogchen adept, I'm a bumbler who read a book about some aspects of it while researching something else entirely, so don't think I'm trying to teach something about a system I don't understand. This is just what I took away from it.
Instead of meditating, you watch yourself without judgment. You observe your thoughts, and where they are coming "from." Fear, hunger, desire, what is the source of the thought? What triggered the thought? Is it coming from your own head, or is it a whispering spirit?
You observe, you don't try to influence or control the mind. You see what you're thinking, and simply practice awareness.
Then, after you've done that for a while, you turn your attention to the observer. Who is it that observes? What is it that is watching?
Remember the words of Perdurabo in the Book of Lies (Falsely Called So):
But FRATER PERDURABO is nothing but AN
EYE; what eye none knoweth.