I am getting ready to get some red lava rock mulch for my flower beds. Right now I have landscape fabric and wood chip mulch on the flower beds. What is the best sequence of events to change this bed from whood chip mulch to red lava rock mulch? Is it OK to leave the current landscape fabric/wood mulch and just place a new layer of fabric and the stone mulch over top of it? I would kind of like to build up the beds a bit around my house anyway. Thanks for your help.