Fool Me Once (смешанная)

Arthur could see his father glaring down - face red and eyes narrowed as he looked at Merlin with clear distaste.
"Once this over, sorcerer...I’ll burn you."
"You’ve already tried that," Merlin’s voice answered and Arthur had to bite his fist to keep from making any noise. “You need to accept you can’t kill me… Hand me that blanket, please.”
“I’m sure there must be some method… Beheading?”
“No, we tried that.”
“Hanging?”
“I just sort of... Swung there, remember?”
There was another pause.
“I should have made you keep that dragon below the castle so I could feed you to it.”
“Kilgharrah? He won’t eat me, but if you want to torture me than making me listen to his nonsense for an hour might do it.” Merlin said and there was a soft sigh from the other end of the room. “I’m glad you agreed to help me though. Usually I have to do the grunt work of saving Arthur myself.”
“I can’t wait to kill you.” 
Or
Uther finds out about Merlin’s magic, but can’t seem to kill him. Merlin is just trying to protect Arthur. They become a begrudgingly effective duo. Arthur doesn't understand why they think he isn't noticing this.