Chagrin:
The low budget approach would be to use a "foam marker". You just need an air compressor, a small fuel tank, and some soapy water. The compressor bubbles air into the soapy mixture and forces blobs of foam out that you use as a reference to see where you've been.
ROFL!!!!!!!!!!!
i have to say this made my night!!!
im reading about GPSes and looks like 3m is about the closest i could get im of to my frend now to disscuss with him if that would be an acceptable tollerance.
from what ive read about GPS protocolls ... i think with a 3m "possible" error and a magnometer it could actually work.. maybe!