Is it common to see pea gravel or some type of stone in the bottom of a valve box? What is the purpose (other that keeping weeds out)??? My contractor did NOT use any. Should I add??? Also, looking into the valve box, it sure appears to be a great place for someone to do major damage to my system if they were inclined. I can just see a couple of drunk kids or even an angry neighbor pulling up wire by the handfull. Is there a way to place a lock on the lid preventing the "honest vandal" from putting me out of commission???? Is this recommended???