Strategically placed near every door, window, sewer pipe, and vent the DM put an Antimagic Field device.
I especially like to imagine a druid coming in through the sewer as a rat and having his robes get soaked in poo when he gets popped out of wild shape.
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.
That could make for a fun gimmick(tie it to a roll behind the scenes) for a session, but beyond that, fuck no. Not only would it be an absolute drag timing out each conversation, eventually the party will start working out ways to get around it, be it a graceful zone of silence to the more likely "Gut the loudmouth and use the corpse as a puppet".
Why would anyone want their diplomacy interrupted, even as the one being affected? It's not like diplomacy is some evil spell. A successful diplomacy check means you were able to have small talk, relate, and do all the normal things strangers do to put each other at ease. You don't "defend" against diplomacy!
Imagine trying to agree on a treaty with some jester interrupting every 54 seconds...
They never really went into detail, their whole argument was that if you wanted to use Diplomacy, you did so by default at a -10 penalty (for doing it 'rushed'), or it would guaranteed fail, for the above reason. :(
Changing others’ attitudes with Diplomacy generally takes at least 1 full minute (10 consecutive full-round actions). In some situations, this time requirement may greatly increase. A rushed Diplomacy check can be made as a full-round action, but you take a -10 penalty on the check.
Antimagic field is an eighth level spell with one hour concentration duration; an item that has it on 24 hours a day would easily be a legendary item. People underestimate how powerful a spell it is and suggest spamming it everywhere. Having it on every door, window, sewer pipe, and vent would be massive overkill just to spite wildshape.
Hiring monodrones is usually cheaper. They are the simplest Modrons, and they would be perfectly willing to work for a Lawful king (the evil-good axis doesn't come into play) because it increases the amount of order in the multiverse. But every modron has Truesight.
Hell, maybe hire a whole team of modrons. Monodrones to stand watch at all ingresses, with orders of "raise an alarm if you see any disguised shapeshifter enter through that window / door / arrowslit / whatever", and duodrones with orders of "patrol the castle and raise an alarm if you see any disguised shapeshifter".