An old dog at it; expert or accustomed to any thing. Dog in a manger; one who would prevent another from enjoying what he himself does not want: an allusion to the well-known fable. The dogs have not dined; a common saying to any one whose shirt hangs out behind. To dog, or dodge; to follow at a distance. To blush like a blue dog, i.e. not at all. To walk the black dog on any one; a punishment inflicted in the night on a fresh prisoner, by his comrades, in case of his refusal to pay the usual footing or garnish.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Dog in a doublet * Dog LatinNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes