(as) rare as rocking horse poo

(as) rare as rocking horse poo

vulgar slang Extremely rare or unlikely; all but, or most likely, impossible or non-existent. Primarily heard in Ireland. An honest person in politics? Yeah, that's as rare as rocking horse poo. I'm sorry to say, but the part this engine needs is rare as rocking horse poo. They haven't manufactured these in nearly 50 years!
See also: horse, poo, rare, rocking