I would like some advice. I am going to sod a 27,000 square ft. area. Before I sod though, I must bring in and grade enough topsoil to fill in a 155' by 40' depression that holds water after it rains. In addition to bringing in and grading this topsoil, I was planning to till the entire area's old turf under using either a power rake or the tiller attachment on a Dingo. The problem is that a sprinkler system is already in place. The poly lines leading to the heads are so shallow in many places that I'm afraid of snagging them while tilling. They are only 1 to 2 inches deep in places. Now, I realize that this was poor work on the part of the irrigation contractor, but how should I proceed to till when the lines are everywhere and so shallow? Furthermore, when raising the grade level in the depression area, should I purchase sprinkler head extensions to accomodate the rise in grade? Any suggestions would be valued and appreciated.