Open leg in London / Ryan Hall triangle ?

I was watching the Video of Eddie & shawn Williams going over London & rubber guard ect. They discussed the hand fighting and the cartwheel pass in London but nothing about passing the open leg. This reminded me of the Ryan Hall triangle DVD where he discussed a lot of scenarios but his bottom leg seemed to lay fairly loose. If the guard player is playing out to one side (like Shawn Williams & Ryan Hall describe) what's stopping the top player from holding strong and stepping over the open leg? Either with just his leg or in combination with his hand.
It's probably a rookie question but I appreciate any feedback

Because the leg would follow you, you can’t simply step over it. If you started messing with it using your hand, you risk getting triangle. If the leg truly was “loose”, then you could, but no one that plays that type of guard will have it like that rolling. Hope this helped and hopefully this is what you were asking :)

Hey I appreciate the reply!
I'm just trying to figure out the exact move or counter because I'd like to try hipping out & attacking from the side. If I'm using both of my arms to hug my knee in London... won't this give him a free hand to help steady my leg for stepping over? Are you saying to break my London grip so I can use my hand to push the arm through?
I uderstand that for the Ryan Hall trianlge he won't have that free hand because I should have wrist control. So you're saying that simply sliding my knee up to follow his foot is enough to counter him stepping?