6-max, 99 vs turn shove by maniac

Pacific, $0.02/$0.04 No Limit Hold'em Cash, 6 Players
Poker Tools Powered By Holdem Manager - The Ultimate Poker Software Suite.

SB: $0.85 (21.3 bb)
BB: $4.30 (107.5 bb)
UTG: $4 (100 bb)
Hero (MP): $4.06 (101.5 bb)
CO: $4 (100 bb)
BTN: $6.44 (161 bb)

Preflop: Hero is MP with 9 9
UTG folds, Hero raises to $0.12, CO calls $0.12, BTN calls $0.12, SB folds, BB calls $0.08

Flop: ($0.50) 4 6 6 (4 players)
BB checks, Hero bets $0.37, CO folds, BTN calls $0.37, BB folds

Turn: ($1.24) 3 (2 players)
Hero bets $0.93, BTN raises to $5.95 and is all-in, Hero calls $2.64

River: ($8.38) K (2 players, 1 is all-in)

Results: $8.38 pot ($0.41 rake)
Final Board: 4 6 6 3 K

The villain is 75/0 from 21 hands, a bit on the maniac side. 67% fold to cbet, Afq: 43.5%

My question is if I could find the fold button OTT. I know that double barreling 99 here is a bit optimistic, but judging by his playing style and the fact that he plays almost every hand, I thought that it's OK vs this opponent.