Clue: Classic question concerning our security arrangements (3,6,3,9)
Answer: WHO GUARDS THE GUARDIANS
Explanation: Definition: Classic question
Cryptic definition – this "classic question" is perhaps better known (well, to me, anyway) in its Latin form "Quis custodiet ipsos custodes?", originally from the poet Juvenal, but eternally relevant. This English version allows a play on the word "Guardian", hence the "our" in the clue