You can peg them out on the ground with old camping pegs or bent wire, under areas you want to remain weedfree, like paths. The woven material means water will disappear, but the weeds won't grow through. We used to get giant - truly huge - old fertiliser sacks from the local farmer, split open they were about the size of a small living room! and use them under all our gravelled areas at home. The only places we had to weed were round the edges - perfect and free.