arusr:
Interesting problem. You didn't give a very thorough description of the two arduinos - are the portable Arduinos? Outside w/ view of sky? On some kind of track where you can set up posts?My first idea is to use a GPS module in each and transmit the location to each other. That'll get you within 10 feet if in open sky. From there, maybe use ultrasonic distance sensors to fine tune the distance off of posts that are set up every 10 feet? Basically, the GPS location tells you which post you're near, and the ultrasonic sensor tells you how many inches you're away from a known post?
GPS on each would give +/- some error each. Those tolerances may accumulate. 20 feet.