To get strong anchor points on the beach, there are bags full of sand. There is also the plate burried in the sand.
All to do is to dig a hole, 20 to 30 cm deep, to place there the plate with a rope fixed on it, and to cover it with sand, caring to have the rope running out. 
Aluminum, 2mm thick, triangular 400x500mm with a rounded side; also used as a showel.
Uprooting over 100kg.
The rope is fixed in the center, or better at the third ahead of the plate. Some tie a float to the tip of the rope, and go back to the mooring the next tide.


The plates do not need to be thick, neither heavy. A plate 20x20 cm will already hold 20 to 30 kg. The uprooting force depends on the size of the plate, of the depth of the burying, of the nature of the sand, dry or wet.
A perforated plate has practically the same effect than a full plate which lead to lighten the large plates for the most powerful kites.
Stainless steel plate Ø400mm, recovered from cut scraps.
Uprooting over 100kg.