Underground Fencing

My yard is fenced in so this really doesnt apply to me, but I just wanted to know what you all thought about underground fencing for dogs. A woman I work withhas a rott/boxer mix that is 6 years old, and she has that kind of fencing with the collar the dog wears so it will get a shock if it trys to cross the boundry. She told me that she didnt realize until a week ago the battery went dead in the collar and her dog was leaving the yard after she went to work, and going and playing with the neighbor kids during the day. By the time she got home he was always back in the yard. The neighbor told her what was happening and she replaced the battery. The dog after she left for work attempted to leave the yard and did so successfully but apparently got quite the shock cause when she came home the neighbor said her dog was hiding in the neighbors garage and wouldnt come out. It apparently really freaked him out, and after she removed the battery and tried to bring him back into the yard he fought and cried. She said she never saw him like that before and she felt terrible cause he didnt understand what had happened, and hid under the porch for the rest of the day. Doesnt this seem like a cruel way to keep a dog in the yard? I don't know much about this kind of thing but it just seems wrong somehow. Have any of you ever used this method with success?