If you have position on him, I'd say go with michael's advice for the turn action. On the turn is where you'll know exactly what you're working with. If you bet 200 into the 500 dollar pot and he cold calls then a draw is likely and its much more likely for the draw not to hit. You have to fire a strong bet on the river though, as he may call down a weak river bet with a random pair he caught when missing that draw. If he reraises you on the turn, it is hardly ever a bluff and you just have to let your bluff go as you no longer have the room to represent your bluff.