This is a technique that we were working on in December in our Advanced Class.
Simple, easy, and no fancy movements. It may not always be a position that you get the first time setting up, but if you get used to looking for it you will find it when attacking an armbar from side control or mount. It is a counter to certain escapes. So learn it, drill it, then when sparring look for it.
Good luck and See you on the mats!
Carlson Gracie Indianapolis Jiu Jitsu 
916 E. Main St.
Greenwood, IN. 46143