this technique is for when you lost control of your opponents foot but still have your legs around their leg. most people give up the leg because their partner is retreating but you dont have to. the trick to this submission is not allowing your butt to scoot in, but instead let their leg be as strait as possible... the opposite of the standard ankle lock. this entire situation could be avoided if you controlled his other leg in the first place. (see my article on : leg control)
you are in a good solid leg control, but you lose control over his other foot.
they free their foot
they push off of your butt with their free leg and pull their foot out of your armpit. you still have your knees squeezed around
sit up. let your but scoot back even further and reach your hand in around their ankle. secure a tight ankle lock grip. shoulder back and elbow back. elbow bent less then 90 degrees. hold tight.
place your inside foot on their thigh, and your other foot over their leg to keep their hip from coming up. when you lay back be sure to pull their leg, and not let your butt scoot back in. you want everything to be stretched out and then pressure to got up through their ankle toward the sky by your wrist.