There were 2 rear naked chokes during the UFN - Marquardt vs. Palhares
They both were completed by trapping one of the opponent's arms. I have been having difficulty with the move in training (specifically with one dude that will just give up his back because his defense is so good). I will start trying to trap an arm myself - Penn vs. Pulver style:
I am not slick enough yet to do the Penn vs. Florian trickery. Give me time.