"We can't just get rid of him!" Merlin objected to Gaius.
"He's a turtle, Merlin."
"He can be a watch turtle!"

Merlin had grown quite fond of the reptile. After all the work he'd put into finding him, Merlin wasn't about to toss Fred out the door.

"A watch turtle?" Gaius asked skeptically.

"Yeah. He can be an alarm. Maybe."

Gaius sighed and crossed his arms.

"Just don't let him into my herb stores."

And so the Turtle Alarm System was implemented in Camelot. Needless to say, it was rather ineffective. But it was no worse than the city guards.