Green’s Dictionary of Slang

1. the stripping and throwing naked into the street of a prostitute by the sailor to whom she has given venereal disease.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Docking. A punishment inflicted by sailors on the prostitutes who have infected them with the venereal disease, it consists in cutting off all their clothes, petticoat, shift and all, close to their stays, and then turning them out into the street.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

2. bettering the condition of a run-down horse in order to improve the chances of selling it.

1821

‘An Amateur’ Real Life in London I 246: If you have a horse you wish to dispose of, the same school will afford you instruction how to make the most of him, that is to say, to conceal his vices and defects [...] to alter his whole appearance by [...] Docking — by patching up his broken knees — blowing gun-powder in his dim eyes.