At our last house we had a system similar to the one Andy described her neighbor as having - No fence involved, just an invisible barrier with the master device in our garage. We trained our favorite sanity saver from the beginning that as long as she had a leash on, it was safe to leave the yard. We didn't have any problems with her being afraid to go on walks with us.
The system worked great for keeping her in the yard as long as the batteries were good. There was a very low beeping sound transmitted from her collar when they began to drop dead. If my favorite sanity saver heard this sound before we did, she would take baby steps down the side of the hill closest to her best friend's house, a German Sheppard. She knew that when she heard this sound, she could safely cross over into her yard. Just to make sure, she always took those baby steps before running to great her. Our neighbors' had the same kind of system for their German Sheppard.
The main drawback besides our favorite sanity saver being smart enough to realize that the beeping sound meant freedom, is that every other animal in the neighborhood could come into our yard. We had one neighbor who had a dog who loved to travel all over the place, hated other dogs, and would try to attack them in their own yards. Long story made short, this neighbor learned that she had to keep her dog in her own yard if she was going to be able to keep her at all.
Even with these issues, we liked having the invisible barrier because our dog never roamed past the German Shepard's yard when the batteries died. She isn't too adventurous and always preferred to stick close to home. Although keeping other animals out of the yard could be an issue, when our dog was outside, we always kept an eye on her from inside. It was nice being able to let her go out on her own in nasty weather. I really miss this now, especially when it's super cold or pouring out!
If I could, I would install this sort of system where we are now. SFR