I have a customer with bermuda in the front and st. Augustine in the back. There is a big tree on one side of the front preventing the bermuda from getting enough sun. So now he wants the whole yard to be st. Augustine. Do I need to till up the whole front (yikes, big job plus sprinkler heads to worry about) or can I just scalp and lay down the new sod on top of the bermuda? That seems almost too easy and it has to be done right or I'll be paying down the road.