Set in Season 5. Very AU. Merlin did something stupid, revealing his magic, probably washing floors or something. Let's assume Arthur actually took it well. At first.

"Merlin, if you tell me there's anything else you've been hiding from me, I swear you're spending the day in the damned stocks, magic or no!"

"Did I mention that I'm the one who hatched that white dragon we saw in the mines of Ismere?"

"…"

"Arthur? Arthur? Ow! Let go, you prat!"

"Sire, why are you dragging Merlin by his ear?"

"Because he's a cabbageheaded idiot who is going to spend the day thinking about everything he's ever done to annoy me, Leon."

"Arthur, you're- Ow! You're being unreasonable."

"Shut up, Merlin."

"Arthur!"

"Stocks for two hours or cells for a week? Because I'm a wise and just king I'll actually give you the choice."

"You couldn't last a week without- Bugger! That hurts!"

"Stocks or cells, idiot?"

"Arthur? What in the world is going on?"

"Hello, Guinevere. I'm just teaching Merlin here it's not wise to hide things from his king."

"Um, alright. Merlin, are you alright?"

"Oh, sure, Gwen, doesn't hurt a bit. Fu-"

"Stocks or cells? Last chance or it'll be both."

"Fine! Stocks, but only because the last time I left you for more than a day you managed to trash your rooms so badly it took two days just to set them to rights. I can only imagine what they'd look like if I was away for seven days."

"Don't worry, Merlin. Now I know you have a way to get your chores done in half the time. So, stocks and cells it is."

"Oh, come on!"

Don't worry, Arthur won't leave him in the dungeon for a full week. He's practically helpless without Merlin.

Also, upon further research, I found that in the 1800s, France had a legal limit to how long a person could be in the pillory of 2 hours and the standard punishment in England was only an hour by then. I apologize to poor Merlin for sticking him in there for four hours in the last chapter. Kudos and thanks to Mersan123 for catching that. I'll be more careful going forward.

My mother used to tell me about one time she pissed off my grandfather and he gave her her choice of punishments; spanking or sitting on the porch watching her friends play. She was stupid enough to tell him she chose spanking so she could go back out to play. She ended up getting both punishments. That was all I kept thinking about as I wrote this.