If I stuck two earth rods in a uniform field (e.g. a big flat area with grass or whatever) at ever increasing distances (e.g. 10m, 20m, 30m ..., 1000m etc) how would the result vary as a function of distance? An obvious answer would be linear (i.e. of the form R = AL + B where B is the resistance of the rods themselves). But a field isn't a wire, it's a plane - and that's a bit beyond my intuition, and beyond any easy maths.