Sand anchors are a great way to secure your kite lines to when flying on a beach or a river bed.
Below here you can see a draft of how to put one together.
Basically you cut a piece of fabric, heavy nylon, 1 mtr x 1 mtr. Then after hemming the square al around, sew two long pieces of 25mm webbing, each 3.5 meters long cross wise on the 1 mtr x 1 mtr square.
Then sew loops on all four ends of the webbing. This will help place a carabiner or such in later on to hold the line in place.

Basicaly that is it. To use, just dig a deep hole in the sand and place the anchor in it, webbing side down, and fill the hole up and pile some more sand on the top.

Gather the ends and place a carabiner in there to tie your line on to.

Click on the small image below to see a more detailed image of the plan.