I am having some problem when in half guard in top position when my opponent gets an underhook and comes up. What are some good counters as soon as they get the underhook. I usually drop my weight down over them, and maybe get the near side underhook and try pass to the otherside with my knee crossing their stomach. Or I try wizzer, the problem I have with the wizzer is that if I use it too early by centre of gravity is too high and they can trap the arm and sweep me back over them. Or if I let them turn into me and get a strong wizzer they are still in a good position to get their legs our and possible come to their knees. This is no-gi by the way.