364 days a year the administrators may impose rules, but dedicate this day to the seniors. Frisking and searching people takes a great deal and, according to the administrators, time is of the essence. Regulate only for safety. If an action is prohibited, students will only want to do it more. The ceremony is supposed to be a celebration not a lecture.
Most students choose to do outrageous things in order to identify themselves to their parents.
Parents appreciate this. If time is the problem, start the ceremony 30 minutes earlier and the departmental receptions 30 minutes later.