Ah, silly dimonds, didn't notice the board went flush

That would surely tip off the aware player on the turn. Since he called on the turn it's pretty safe to say he's not very aware or has Kd. But you have Kd. So he doesn't. So he's not aware. Save yourself $5 and don't fire the second barrel. Then open up the player notes and say "don't bluff this guy".

In other words, now that I'm reading the hand right - good turn, bad river. This guy just wasn't ment to be bluffed...and there might very well be a lot of those at your limits, but surely not all.