as above the stuff you put down on garden to stop weads growing and allowing you to put pebbles over top

Try your local allotment society as they should sell landscape / weed
surpressing fabric cheaply.

If you just put visquene down, then water won't drain away through it. Better to use a weed-surpressing membrane. I got a huge roll of the very heavy-duty stuff from eBay, and it's great stuff. Nothing grows through it, but it won't get waterlogged.