[Magnectic Sensor]

Can a magnectic sensor senses a perimeter wire which is in a close loop circuit?? ???

[Robotic Lawn Mower]

Hi... i and a group of 4 r now doing a robotic lawn mower project and now we r suffering a serious prob.... Is it better to use a sensor for the navigation system or a RF circuit will do? I tried to search the net and i found that almost all the robot lawn mower r using sensor but now our group r using RF as our supervisor encourage us to do so...
  So... can anyone tell me is it better to use sensor to do or RF??? if so, can u pls give me some ideas of how to use it?? thx....