The key to defending Knee on Belly is by keeping your elbows tight, blocking the underhook and reacting quickly. Opponents with good Knee on Belly pressure is not enjoyable. It should be your focus to get to your side, facing towards your opponent as to not expose your back. When on your side push off of their knee and shrimp at the same time. From here you can transition to open guard or push the knee down and collapse into Bottom Half Guard.