No irony intended, just brainstorming thoughts. Russian/Canadian.
Other idea I did not implemented in project yet, could be slightly modified version of this hardware: http://coolarduino.wordpress.com/2012/07/28/visual-navigator-making-it-mobile/ 3 leds or lasers can be assembled spatialy apart (20 cm or so, as road / traffic sign) as a sign unit, visually visible from 10-20 meters (depends on power, lighting conditions etc) and again, installed as a beacon. Arduino can see a "sign" as 3 dot , calculate distance to and plane angle to sign. May be not very accurate with chip CCD cam, but optical zoom (20 - 30 x) would bring accuracy to inches or better.