Wire following

Hi,
I want to install a special feature on my 6x6 robot. I want to install a wire detection to follow cable under carpet.
Which sensors do you recommend? Which method did you use? The cable have to be in boucle?

ANd what about this stuff:

http://www.befr.ebay.be/itm/CLOTURE-ELECTRIQUE-COLLIER-ANTI-FUGUE-CHIEN-NEUF-/180629282906?pt=FR_YO_MaisonJardin_AccessoiresAnimaux_PourlesChiens&hash=item2a0e58205a

Thanks a lot

Max