I actually haven't heard about any Yorkie owners using electronic confinement... sorry, perhaps someone else may have?
But I did find these two products, perhaps you can call them up or email them to see if it'd be suitable for what you are looking for...
http://www.petsunleashed.com/petsafe/prods/PIF-300.html http://www.petsunleashed.com/petsafe.../RF-3004W.html