I'm sorry, but I'm going to have to disagree with some of you. Though an IF isn't an ideal situation, some people are not allowed to have fences. IFs are another option. Like I said earlier, they are not perfect for everyone. My parent's dog, Greta, has probably been shocked 2 times in the 3 years that they have had the fence. I've accidently stepped on her foot a lot more times than she has been shocked. Before my dad even put the collar on her he shocked himself with it first. He said it was uncomfortable, but didn't really hurt that bad. The collar is only on her when she is out in the yard, otherwise it is taken off and put away. The collar gives off a noise when the dog gets within so many feet of the boundary to warn the dog before it gets shocked. My parents could probably shut off the shock and she would stay in the yard just hearing the noise. Again, I'm not saying an IF would work the same for every dog, but for my parent's it has worked just fine and Greta is a very happy, healthy, spoiled dog. But if given the choice, I personally would prefer a regular fence to an IF.
Edit to add: Almost all of the horror stories of invisible fences (or all fences for that matter) could be avoided if people supervised their dogs instead of throwing them out in the yard and leaving them to their own devices for hours on end. JMO