Ditto Rob..........I do the exact same thing as you, except my sand anchor, doesn't have all those rocks in it, just nice, clean, heavy, sand.
On big, hard pulling kites, I use a pulley on the line, to walk the kite down, especially if it's really blowing. Once you have walked the kite to the ground, you disconnect the kite, and then there is no pull on the line, as you wind it up..........if the wind isn't blowing too hard, or the kite isn't to big, I just slap a carabiner on the line, and walk it down..........