More on Sound as a Roach from Infoplease:

• Sound as a Roach - Sound as a Roach Quite sound. A pun upon roach or roche the fish, and the French roche, a rock. ...
• Roach - Roach Sound as a roach (French, Sain comme une roche). Sound as a rock. Source: Dictionary of ...
• Similes - Similes in common use: BALD as a coot. BITTER as gall,soot. BLACK as ink, as a coal, as a crow ...
• Dictionary of Phrase and Fable: S - Definitions, origins, and illustrative excerpts for words, phases, and literary allusions starting with "S"