when I built my house 14 years ago, I put down sod and had a very nice lawn until 3 years ago. Crabgrass has taken hold on about a third of the area (approximately 400 sq ft). For the past 3 years I have applied pre and post emergence products, with no success. I now want to remove the affected area with a sod cutter and then re-sod: 1) how deep should I cut the sod to accept the new sod? 2) there should be a good layer of top soil left after the sod is cut. Should a top dressing of some type (i.e.more top soil) be applied ? 3) should I apply a crabgrass prevention agent (either pre or post emergence agent) before putting down the new sod? and if so, how long should I wait to put down the new sod? 4) what is the latest time to start this process this year?