Originally Posted by Ben Langford
The guard break you are describing has two key components - pinning your opponent's hips to the ground and opening your hips wide after you've stuck your knee against their butt.
I think Ben has the key piece here. Most often when I see people struggle to break a closed guard in any fashion it is because they are allowing their opponent to move their hips to retain the guard. Yael also made a similar point in that you don't want them on top of your knee. If they are there their hips aren't on the ground and you will have a harder time breaking the guard. With their hips firmly planted you can increase the pressure significantly and most often get the legs open.
The other question is does this particular opponent have a significantly different body structure from others in the academy. Meaning does he have really long legs that allow him to retain closed guard where others couldn't? If so look at different ways of opening his guard. For really long legged people I love the standing guard passes.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin