$100NL, Full ring on UB. Opponent has been playing 50% of hands, has been calling almost any raise and has been raising whenever it was limped to him. He's been trying to steal whenever he has the chance, and is not afraid to bluff huge, or call big bets extremely lightly. He's also been catching some hands and of course got paid on those. He has a $300 stack, I have about $200.
I've given up a lot of pots to him because I've been missing flops completely, so he probably perceives me as weak and/or scared. I've tried various things such as leading into him, checkraising him, but he almost always came over the top huge and I had to fold.

I have [8s] in LP. Villain raised to $4 from EP, I call, BB calls (he's only got $15 behind), rest fold.
Flop: [5s][9h]. Villain leads for $12, I make it $35, BB folds, villain quickly calls.
Turn: . Villain leads again for $30. I call. (Anyone push here?)
River: . Villain leads for $60. I'm considering a bluff raise here but chicken out, as I think he'll call me with any pair. Correct or chicken?

And a general strategy question for playing such an opponent. Assuming that you will not make hands with any showdown value, what kind of situation are you looking for to steal a pot from him? How many BB are you willing to risk on a pure bluff?