I never heard of any tarps that ALLOW dirt and water thru...doesn't make sense to use a tarp...a net maybe, a tarp is ment to keep those things out. Do you mean KEEP those things out? There is some material that allows AIR thru but not dirt and water. http://www.farmtek.com/farm/supplies/prod1;ft1_haytarps_covers_pondliners;pg106429
Yes its a new tarp that came out. It allows water, dirt and sand to go through, but does not allow it to come from the ground side back to the top surface side.
contacted the company as I wold love a larger mat like they have for the RV use in OZ
he said they are thinking of introducing them in 2012
would like a large 12x24 or so size