After you get the mount (probably from a clinch and a takedown), there's a pretty good chance the attacker will try to push you off. One way is that they may try to push your shoulders.
Now, if you lock up, they will succeed getting you off of them. But, if you turn your shoulders and swim one arm through and then the other, you will successfully neutralize that attempt.
You also should bring your knees up a little, and go heavy on their hands, almost like a cat that doesn't want to be picked up. Bear your weight on their hands, swim one arm through their arms AS YOU TURN YOUR OTHER SHOULDER AWAY, just like the motion for swimming, and then bring the other one through.
Once you've done that, spread your arms and get lower. They'll either give up, or change tactics, which are completely predictable.
It's a simple, yet highly effective maneuver.
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