Buried Wire containment system

[BillericayBoy]

Hi, i am looking at building a containment system like the ones used on invisable dog fences. I have found a couple of robitic lawnmower sites that use the system and wondered if any one here had built their own containment system and could give me any pointers.

Basically there is a transmitter which has a large loop of wire, along which a signal is sent. then the robot has a sensor (like inductive giudance) to pick up the wire when it gets close and to trigger a stop routine when the signal strength has peaked and is reducing, allowing a reverse and turn command to be run.

Thanks

BB