|Either in the middle of a Grambi Roll or a two-man breakdancing routine|
Keeping your opponent in between the imaginary lines coming out of your knees is one of the most basic aspects of guard control, if not the most basic. The Grambi Roll is the easiest method to regain open guard control against an opponent who is standing and actively trying to pass your legs to land in side control.
All of you blossoming butt-scooters out there, take note.
As you see your opponent reach for your ankle and step through, bail on any grip you have on your opponent, tuck your far elbow in, turn away from your opponent, swivel your hip toward your opponent and up, and swing your legs around to regain guard control. From there, get your grips back.
While this is all very basic, I have seen some very cool triangle setups off the Grambi roll, so maybe something to look into.