Green’s Dictionary of Slang

(Aus. prison) a punishment cell; solitary confinement.

1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxv 6/2: huckleberry: A pound, named after Huckleberry Hound, a cartoon character.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 31: Huckleberry Hound Pound (isolation cell in prison).
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Huckleberry Hound. Cell. Rhyming slang for ‘pound’.