Many of the BJJ competitors at the black belt level have an open guard that at times seems to be “impassable”. A good example of someone with an “impassable guard” is Michael Langhi. Here’s an example match of his against Gilbert Burns:
Basically, it’s a remarkable mix of flexibility, agility, grips, leverage, and instinct that allows the player to keep his legs and hips always between him and the opponent.
Michael Langhi is one of many such guys. The “impassable guard” is a relative concept. For me, a lowly blue belt, a lot of guards are “impassable”. As I slowly progress, learn, and evolve, one by one I start to figure out the details of passing those guards. So the goal is always to pass the guard today that I couldn’t pass yesterday.
I think the following video of Mendes brothers loose guard passes really demonstrates the key challenges of passing a good open guard. It’s a mix of solid technique, constant pressure, aggression, balance, base, and follow through. It seems to me that the hardest part of passing is finishing the pass. I can often execute the leg drag effectively, but capitalizing on that position to gain and hold side control is a whole another battle.