We have 2 dogs. A Corgi and a Yorkie. We have a hidden fence by a company called Petsafe Hidden fence. We had it installed in September. Our Yorkie weighs 7.9 lbs as of Friday and he wears his collar quite easily and comfortably. He enjoys the outdoors alot and had no trouble at all adapting to our system. He has zero aggressive behavior and has an amazing personality. He is not at all bothered by our system. The Petsafe system gives an auditory warning in a wide zone in front of the buried wire. He doesn't usually get beyond this and when he gets the warning beep from his collar he just heads back into the yard. We personally have been very happy with our petsafe hidden fence for our Yorkie. I especially like it in the front yard so he won't go near the street.