How about taking a nice long coil spring and giving it a point at one end. Weld on a cross bar type handle, and "cork screw" it into the ground. You could weld on a ring at the top to attach the winch cable to while you're at it.
I got this idea from the tie out for my dog. He can pull over 2000 pounds on a runner sled, and these types of things can hold him in one place.
95.5 YJ with "stuff"