This is my favorite guard. Break his grips, avoid letting him get the near overhook especially in a gi - if he has the overhook and is gripping your/his lapel you're getting swept to your back 95% of the time. You can try stuffing the leg but it's easy to create space and regain the Z-guard or transition to deep or traditional halfguard. Regain your posture. If he has crossed his feet then you need to get them unentangled. Then stand (usually I go to DLR or X-Guard when this happens) and try not to get dragged back into the Z-guard. Also, don't let them get the shin across and kneebar you, or get the near underhook to try to take your back or sweep. Don't let them touch your legs generally either. You should really try to disengage rather than pass the Z-guard. Hmm, yeah . . . very difficult guard to play against.