Basic cheap drugstore cotton string. Two 5' +/- lengths with a knot tied in each end so they don't unravel. Tie onto suspension inside the tarp edge. Drop hanging end into water capture reservoir (bottle / pot) or lead em back outside the tarp edge. They only weigh a gram or two and wick like nobody's business.
"...the wolf shows up. Then the entire flock tries desperately to hide behind one lonely sheepdog."
-LTC D. Grossman