[FlyingBeagle]

A trick I learned a while back is to cover the area of grass with a few layers of news paper then dampen it with water so it will stay put while you are putting soil, gravel, or your cold patch down. The grass cannot penetrate the paper and will die out. Eventually the paper will biodegrade but the grass below will already be dead and will not grow up through the surface. I use this trick when installing new flower beds over existing grass or when building raised gardens out of railroad ties. It works every time.