Question
Hi There, Have rodent/vole/gopher damage in part of my lawn resulting at a
large area that has sunken below grade a couple of inches due to the tunneling.
How can I bring that area up to grade again without killing the grass there?  

Answer
It requires patience. You apply sand in a thin layer, allow the grass to grow out of it and repeat the process until the area has reached the proper grade. It is very important that you do not smother the grass; all you want to do is cause rooting in the layer of sand that you have provided. I have never had the patience to do this; I end up resodding.