The standard initial kneebar defense is to just figure four your legs so that the leg being attacked is underneath. It's far from foolproof but it can buy you a couple of important seconds. I was once shown a counter to the figure 4 where you can somehow turn it into a completely different leglock. I don't remember if it attacked the foot or if it was a calf slicer to be completely honest, as I was shown the technique when I was a very new blue 4 years ago, and didn't know fuck all about leglocks. Anyone have a clue what I'm talking about?