Strategically placed near every door, window, sewer pipe, and vent the DM put an Antimagic Field device.
I once played with someone who argued that Diplomacy would never be usable on any important person because, since it requires 1 minute of uninterrupted conversation to use, everyone who is important enough would have a jester or aid or someone they'd hire specifically to interrupt every conversation they were involved in every 9 rounds. Absolutely infuriating person to play with. This anecdote is completely unrelated to this post, but your suggestion just made me remember it again, and it irritated me all over again.