For example, you can add sand to prevent tiny breaks or lines from forming in the finished product.

VOA: special.2009.09.14

The same powdery sand also lines the northern beaches of the facing island, Haslewood.

BBC: Kayaking Australia��s Whitsunday Islands

This highlights the trouble with lines in the sand: sometimes the tide washes them away.

ECONOMIST: Reaction to Sarbanes-Oxley

Now, given his post-election lines in the sand, he wants to rub that sand in.

FORBES: The Fiscal Cliff: Why Sticking It To The Rich Will Hurt Everyone