Pretty much what I was doing Mole, but I used a standard flat blade shovel. The problem with following my back fence is my neighbor has ivy that grows through my fence, I had to chop through the ivy, and all the roots in my soil just to get a shallow trench to bury the wire. either way I do it, it's labor intensive.
I'll add more radials over time as I find more scrap wire, and the inspiration hits me to do it.....