retired

if your in control (your gloves are on the top/back of his head) any time he goes to knee you pull his head toward his attack eg:
if he goes to knee you with side knees then yank him to one side or turn him thus losing his balance and disabling the efectivity of his knee, if he goes to do a lunging knee you will feel his head drop to assist his attacking leg at this moment yank him to the side & you dont have to worry about blocking.
you can sometimes turn your hip towards him and lift your leg with the foot still against your bum and lean it in against his leading leg although you need to watch him carefully cause you'll be on one leg.
if your in control try pulling his face to the floor at which moment you stretch the attacking leg backwards as far as you can reach then drive it forwards into his rib cage, not enough people use this knee & continue with side knee's which aren't that effective in short fights.