I've been using this lately with great success. It's a simple ankle lock for when someone tries to replace guard from sidemount. You are sidemounting someone on his righ side. He turns onto his right side and brings his right shin (the bottom leg) across your stomach. (The standard way to replace guard) Put your left arm over his head to cradle him as you isolate his right ankle with your right arm to go for the ankle lock. This should take no longer than a second or two. Fall back and to your left side while bringing your right knee between his two legs. Squeeze your knees together and you've got a solid ankle lock. Once you get a hang of it, try to do it relatively quick. You shouldn't telegraph it just like any other submission. Make sure that when you ankle lock you're in deep (solid on his achiles) and you aren't giving his foot any space to wiggle out.