Not very movable

Just had a quick thought today about how ridiculous Clark Pinnock's "most moved mover" idea about God is. For those who don't know about Open Theism, Mr Pinnock et al claim that God is not sovereign over time, but is a player in time alongside us, who does not know the future or determine it. He is just a bigger ball on the snooker table of space time than we are. So why does God call himself our "rock" repeatedly through the Bible? The whole point of a rock or mountain is that it is immovable! It is because of this very reason we can fly to God in times of trouble as we know he is ever constant and trustworthy. Does Mr Pinnock not see how dangerous his doctrine is in undermining our assurance?
My Dad is in hospital at the moment, so knowing God's trustworthiness is very important. Do pray for him.