I owned Invisible Fencing with my first pitbull. I didn't own it because I was "lazy."
It was a ton of work to install, and took a long time to train him properly on it. He was a rescue dog with unreal seperation anxiety who could not be contained and just wanted to run. It cost me a fortune and I probably had somewhere around an acre 'fenced.'
The idea isn't for the dog to get 'zapped' everytime they leave the yard. People who don't know how to train their dog or are indeed "too lazy" to train them use it like that. The idea is to train the dog to acknowledge a boundary visually (with the use of flags marking the perimeter), and by a beep that warns them if they are too close to the boundaries. The 'correction' if they go through can be set to different levels, and mine was set on the equivalent of hitting your finger on a plug prong while plugging it in---startling.
My dog was on it for over ten years, only went through it and got 'corrected' once while training, and never had an issue with any other animals or people, (aside from the occassional loss of a squirrel or frog.)
Mine would only have gone through it IF I forgot to change the battery, but the company had a battery program that sent you batteries usually before you even needed them.
My guy's seperation anxiety vitually disappeared after being on I.F. You should, however, make a good assessment of your dog and whether I.F. is suitable for them, and proper training to the perimeter and the warning beep are the KEY. My current dogs are not on it.