nano-limit 99 vs calling station

[checkmate36]

PokerStars 0.05/0.10 Hold'em (9 handed) internettexasholdem.com

Was dealt 99 3 different times in todays session and would be interested in any comments on this one. My opponent is rated as a calling station with a VP$IP of 58% and PFR of 4%. Thanks for any thoughts on any street.

Preflop: Hero is CO with 9[img]/images/graemlins/diamond.gif[/img], 9[img]/images/graemlins/club.gif[/img].
UTG calls, UTG+1 calls, <font color="#666666">1 fold</font>, MP2 calls, MP3 calls, <font color="#CC3333">Hero raises</font>, <font color="#666666">3 folds</font>, UTG folds, UTG+1 calls, MP2 calls, MP3 calls.

Flop: (10.40 SB) 6[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/club.gif[/img], 3[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
UTG+1 checks, MP2 checks, MP3 checks, <font color="#CC3333">Hero bets</font>, <font color="#CC3333">UTG+1 raises</font>, MP2 folds, MP3 folds, Hero calls.

He probably has a 3 with his c/r. You never know what these guys are thinking and I decided at this point to call him down to the showdown.

Turn: (7.20 BB) K[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG+1 bets</font>, Hero calls.

River: (9.20 BB) 5[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">UTG+1 bets</font>, Hero calls.

Final Pot: 11.20 BB

What kind of hands has villian shown down with aggression? It looks like he is trying to protect his hand, if he is that smart, so I might 3bet the flop or call the flop and raise the turn. I don't know if I really like calling down, especially if he is on a diamond draw with two overs. I want to make him pay on the turn, and then a free showdown can be taken if desired.

Any reads? What's his total ag # look like. If he's microscopic in the aggression dept. I'd call the flop raise, and possibly fold the turn UI.