This is because of the amount of space an owner can give to his dog and the fact that the dog can not walk out of this perimeter without an electrical correction.
A wireless dog fence works on the principle that the owner gives the dog a specific amount of space to roam in. When the system is set up the radius can be set by the owner and the dog can be trained to stay within this radius by ways of using the techniques that come with the system or training by the owner itself.
The dog will be required to wear a specific dog collar that will have a sensor in it that detects the perimeter set out by the owner of the dog.
You can at all times increase or decrease the perimeter set out in the invisible pet fence so that you can give your dog more "leash" or less, depending on your needs. This way you have a good system set up that will allow your dog to walk around freely within the perimeter, but you can always adjust it so that the dog will be confirming to your needs.
If you have set up the system by simply plugging it into the electrical socket and setting your range you can start using it. At this time you should have already trained your dog with the instructions provided so that the dog will adhere to the boundary.
Now you can give your dog its new collar and let the dog run around as much as it wants. As soon as the dog closes in on the edge of his territory there will be warning beep that is transmitted from the dog collar. This will teach the dog that he is close to the edge and if he fails to listen to the beep and wanders further away and into the disallowed zone, there will be an electric correction.
With these corrections come small electric pulses that will get the dogs attention and teach him that what he did was wrong. As long as your dog listens to the electronic or electrical signs there will be no problems at all using the wireless electric dog fence for many years to come.