A lot of us who take up kiteboarding are "natural born tinkerers". We appreciate creativity. This idea is quite creative, and it could be sold not just to kiters, but to any number of beach goers, who now take hundreds of dollars worth of electronics to the beach. These "sand anchors" could become a part of normal beach-goers beach kit. Just imagine the "assessories" that could go along with this idea... waterproof lockable boxes designed for i-phones, tablets, wallets, a "screaming mimi" divice that screaches when someone touches your stuff (you just have to come in off the water and punch in the code that silences it... I don't see any problems with that... other beach-goers will understand)!
The trouble in the future, where lots of this kind of stuff on the beach would immediately indicate to beach theives exactly where to valuable stuff is located..... is that....with a "vice-grip", the thief could easily unscrew the cork-screw anchor.
The dangerous problem, though, for kiters, is that there would be a lot of stuff on beaches that would not move when a kite line snagged it. At least now, when a line snags on something.... most of the time the line flips the item over and clears itself. So, the device should have a "quick-release".
But getting back to making it hard on thieves... what you really need in order to make the anchor more un-removeable is... TWO stakes which are locked together, so that neither of the stakes can be unscrewed without haveing the other stake rotate around and around the first stake. This could be done most easily if the "T" handle of each stake could slide through a ring in the top of the stake, so that it could be positioned in the center when the stake was being screwed into the ground, and then, the handle could be slid all the way to one end of handle. This way, the 2 ends of the handle would slide together and a padlock could connect them. Here is a picture.
Lots of problems with the whole concept of attaching stuff to a beach... tripping, snagging, etc.
I will just keep putting my wallet and i-phone in my shoe... they will never find it there! ha,ha,ha