TreadBot

[mackrackit]

this is a neat idea, a little expensive for hobby robotics though....

http://www.robotshop.ca/home/product...ar-system.html

Looks similar to Skimask idea, I was going to suggest sonar also. I have a cheap sonar measuring tape that is pretty accurate. Use two to have a location.

Let us know what you plan to use and we will see if we can help.