I believe I read that at the Borghese Gallery, among other places, in order to rent the audio guide, you must leave them your passport, etc. (I assume so that they know you will return the audio?). Am a bit concerned about leaving our passports in exchange for this at various sights -- if it gets lost, misplaced, given back to wrong person, we could spend a lot of our scheduled trip getting replacements! Can we leave a driver's license or our 'expired' passports instead? Thanks for your thoughts on this topic.