I put down 240 radials for a 4-square on a piece of densly forested land
that had been cleared for the purpose. There were lots of roots, stumps and
debris. I used bare #16 copper wire. For staples, I used the largest bobby
pins I could find. The bobby pins were surprisingly effective. Even on this
sort of terrain, radials do tend to bury themselves over time. There are
still some areas where I can see the radials, but most of the wire is under
a layer of loose soil, debris and vegetation.
73, Dick WC1M