I made a holddown much like Bingo Flyer's except it's made of 1/2 inch copper water pipe.

(2) Uprights about 15 inches long, (2) 90 degree elbow joints, (2) short sections of about 3", (1) "T" joint, two end caps (on top), (1) pipe length of about 12" for the bottom of the "Y" and some pipe insulation.

Took about 15 minutes with the propane torch to solder it together. The bottom is hammered flat to avoid it filling with soil and gives it an "edge" to cut into the ground.

I just put it in place with a slight backwards slant and step on it. Works great.