This reminds me of a time, about 30 years ago, when I was teaching. The staff were fully aware that the pupils would try to sneak in a much booze as possible at the Christmas disco. Instead of lecturing them about the possible 'dire consequences' of their actions we simply told them, during assembly, that it was a condition of entry to the disco that any alcohol found would be regarded as a gift to the staff. So we told the pupils to bring as much booze as they liked because the teachers would all enjoy drinking it!
This was back in the days when the 'Mods' fashion was enjoying a resurgence and Parka coats, with their many voluminous pockets, were all the rage. When the pupils arrived at the disco, we insisted that they must hang up their coats in the PE changing rooms. Once they were all in the disco, a group of staff frisked all of the coats, to see which ones 'clinked' (which most of them did). If they did, we didn't go into the pockets, we simply removed the coats to the staff changing room 'for safekeeping'. We then sat back to await the arrival of groups of pupils who periodically seemed to find the need to 'get something from their coats'. If they found that their coat was missing we invited them to see if we'd 'taken it for safekeeping' and asked them to show us what it was that was weighing the pockets down.
Everything was done in a friendly fashion. There were no lectures, no detentions and no letters home to parents. The pupils enjoyed their disco (and remained sober) and we found enough free booze for 50 staff to have a great party with when the school closed for the holidays on the following day ;-)
Chris