I have an area around the perimeter of a house, where the homeowner wants to rip out the grass, and put a rock border around the perimeter instead of grass. Now there are a few existing rhodi's, but mostly just grass. I want to put something under the rocks so that weeds will not grow through. I have seen some thick black fabric, (not the homedepot stuff) and was wondering if it will work with existing plants? Also where can I find this thick fabric, almost resembles a blue tarpaulin type material?