Since you are digging deep you might consider burying the sod at the bottom. I used this double dig method for creating lovely loam for some beds. Now I just layer cardboard, add mulch and wait. Done in the late summer to early fall it is decomposed and ready for spring planting with little effort on my part. I live in a temperate, moist climate so it works well for me. Smothering the weeds with enough cardboard is the key for my success.