Green’s Dictionary of Slang

pound v.1

also pound it
[the cockfighting practice of offering £10 to 5s, a very extravagant bet which was known as pounding a cock. If no one took it the match was automatically off]

to place a bet that one is sure one will win.

[UK]Vaux Vocab. of the Flash Lang. in McLachlan (1964) 259: Pound it, to ensure or make a certainty of any thing: thus a man will say I’ll pound it to be so; taken, probably from the custom of [...] offering ten pounds to a crown at a cock-match, in which case, if no person takes this extravagant odds, the battle is at an end. This is termed pounding a cock.
[UK]W. Perry London Guide 42: But mark this: provided you make good use of your lungs, and also make a decent stir before you get touched with hand or stick, I’ll pound them to bolt in a jiffy.
[UK]‘Jon Bee’ Living Picture of London 44: You’ll soon be bowled out, I’ll pound it.
[UK]R.S. Surtees Jorrocks Jaunts (1874) 239: I’ll pound it the old tabby carn’t be under one hundred.
[UK]Comic Almanack Oct. 332: At first, wouldn’t I have pounded it he was a real swell.
[Aus]Satirist & Sporting Chron. (Sydney) 18 Feb. 2/2: Look on Brickfield Hill at 5 p.m. and ‘I’ll pound it’ you’ll see the ‘long night-gown’ on his road.
[Aus]M. Clarke Term of His Natural Life (1897) 55: He didn’t hear nuffin, I’ll pound it.

In derivatives

poundable (adj.)

certain, definite, inevitable, esp. as regards the result of a wager.

[UK]Vaux Vocab. of the Flash Lang. in McLachlan (1964) 259: poundable Any event which is considered certain or inevitable, is declared to be poundable, as the issue of a game, the success of a bet, &c.
[UK]Carlisle Patriot 9 Dec. 2: Hudson made a plunge with his rigjht hand upon his opponent’s face [...] followed him up to the ropes, and punished him down — 3 to 1, and ‘it’s poundable’.
[UK]Westmorland Gaz. 21 Dec. 2/3: The 14th round was a ‘quietus’ for Hudson [...] and Shelton was poundable not to be able to get up again.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.