He has had air and exercise, i.e. he has been whipped at the cart’s tail; or, as it is generally, though more vulgarly, expressed, at the cart’s a-se.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Aground * AldermanNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes