online 3/6 hand (any two can win)

[tdiddy]

I usually play 1/2 and 2/4 but decided the 3/6 at pacific looked good. So I give it a try. The second hand of the session this happens:

8 handed 3/6 at pacificpoker.com

UTG: raise
all fold to Button minus 3 (B-3)
B-3: call
B-2(ME)[QsQh]: raise
B-1: call
B: call
SB and BB fold and remaining players call my raise.
FLOP: 6d 7h Jd
checked to me and I bet
button and UTG call, B-3 folds
Turn: 9h
checked to me and I bet
button and UTG call
River: 6c
UTG bets, I call, button folds
UTG shows me 4s 6s and rakes in $85 pot

The bastard raised UTG with 4s6s, how can we defend against this?