You gotta learn to admit that your guard is being passed. There is a difference between having your guard passed and being on the bottom of a bad position, but the window is very small. If he's already passing and you're trying to squeeze your legs together to keep him there, your guard has already been passed (whether you are aware of it or not). Once I figured out that it was my own ego that was getting my guard passed, my guard improved dramatically overnight.
Do not grasp.
Be like water.
As he passes, shrimp to move your hip away from your opponent and then square back up with him in front of you.