My favourite MTS episode, because after watching this I finally, after years of training, 'got' the arm bar...
Elbow on the belly button or beyond = almost 100% game over with me these days (not by Rousey's instruction though, Eddie's). Rousey's instruction is good, but as Eddie says you need to have incredibly strong hips and have repped it thousands and thousands of times to cover such a massive amount of distance so quickly. Anyone any good will pull their arm out or stack you. As soon as I realised this and started to concentrate on locking the shoulder first it truly helped - also, after Brandon's Brackish Waters video (he posted it up pretty recently), when he said you can do it off any shoulder lock it all came together. Shoulder lock - go for the arm, if he/she doesn't give you the arm transition to Brackish Waters then Dead Orchard (my current path).
Note: If you get the shoulder lock and he rips his arm out somehow then the Triangle is right there too.