"The couple respectfully requests that no outside personal cameras be brought into the ceremony or reception. Thank you for respecting our wishes." Send it out after guests have RSVP'd and you are sending follow up stuff like maps, directions etc... Good Luck! If anyone doesn't respect your wishes or are offended by them do they really deserve a spot on your guest list? You can even ask the person who is monitoring the guestbook to put a basket out for all those who "forgot" to check their cameras like their coats.