Standard donkbet defense

[cbloom]

No Limit Hold'em Ring Game (6 max) , 6 players
Blinds : $0.50/$1

Stacks:
UTG : $109.05
MP : $57.30
CO : $61.05
Button : $186.10 (Hero)
SB : $129.60
BB : $107.05

Pre-flop: (6 players) Hero is Button with 9[img]/images/graemlins/spade.gif[/img] K[img]/images/graemlins/spade.gif[/img]
3 folds, <font color="#cc0000">Hero raises to $4</font>, SB calls, BB folds.

Flop: 3[img]/images/graemlins/heart.gif[/img] 9[img]/images/graemlins/diamond.gif[/img] 7[img]/images/graemlins/heart.gif[/img] ($9, 2 players)
<font color="#cc0000">SB bets $3</font>, <font color="#cc0000">Hero raises to $12</font>, SB calls ($9).

Turn: 6[img]/images/graemlins/heart.gif[/img] ($33, 2 players)
SB checks, Hero checks.

River: 4[img]/images/graemlins/club.gif[/img] ($33, 2 players)
<font color="#cc0000">SB bets $10</font>, Hero ???


Villain is typical awful donk, chases, bluffs, etc.

What's his range here?