Thanks a lot for the great info dunk and everyone.
As you said, it looks like this is one of those things that sound like it should be easy to accomplish at first, but reality has other ideas.
I was looking for something quick and simple to set up in the yard without installing tracks or magnets in the ground. I was also looking for a signal that would make life much easier by traveling through objects (houses, etc) like radio waves do. I figured if I threw down a few radio wave beacons emitting a signal and could detect the direction of each one then that would be a very simple solution for making a coordinate system and waypoints for a robot to follow accurately.
This would have been a tough and robust solution that could deal with many different terrains and the robot's shaky movement on uneven terrain. I am probably not interested in using IR or webcam since the bot would always need a visible line of sight to the beacons. I guess that might still be possible but but would obviously require many more beacons in my not-so-level yard.
advanaco, that's a good idea. I do have a fence but it's a split rail
Also, was hoping for an easy, tough, and robust system that could be used in any yard without much fuss.
If i go forward with the project I'll prob either try many IR beacons or try to think of something outside of the box.