Rope Pick And Shovel Compass to Draw Outline for a Desert Rain Catchment Pond Design

I was never the best math or geometry student, I did okay but didn't really apply myself. Only later in life have I realized I wished I'd have applied myself more early on. Luckily a few years ago, a very mechanically inclined friend of mine re-introduced me to the concept of making a compass with a string or rope and a central anchor point such that if you pull the string or rope tight and walk it around in a circle, you'll be able to draw or dig a perfect circle. I can't believe that escaped me for so many years but it did. He was helping me cut a lid for a worm compost bin, and there it was. The most elegant technique. Well, I've adapted that to the larger scale now having dug 5 separate 30 foot diameter ponds. Here I'm using a shovel dug into the center point of the pond. Then I loosely tie a rope to the shovel that's length is the radius of the circle of the pond. Then I tie the other end of the rope to a towel which makes a loop to drop over a pick axe. I then drag the pick axe on the end of the rope in a circle and I have my perfect circle pond outline.