Invisible fences work by giving a dog a warning beep as he nears the boundary of his property, and giving him a slight shock via his collar if he continues on after hearing the beep. The dog soon learns to stop when he hears the warning to avoid the shock. The shock should only be strong enough to startle the dog, not enough to cause real pain. The strength of the fence is changed by adjusting the shock level of the receiver worn on the dog's collar, the warning alarm field of the transmitter control box and the size of the metal prongs used.
Push the button on the receiver. A light on the receiver will flash. Push the button again within five seconds of the first push and the light will flash from one to five times. That will tell you the current correction level. Push it again within five seconds and the correction level will change. For example, push the button; the light with flash once. Push it again, and it will flash three times, indicating a level 3 correction. Push it again, and it will flash four times indicating an increase to a level 4 correction. After level 5, the receiver reverts to level 1, which is a warning alarm only, with no shock.
Adjust the distance from the boundary wire to trigger a warning alarm. Most transmitter boxes have a knob or lever to use to change the distance. The alarm on the dog's receiver should sound no less than two feet from the wire. The farther from the wire the alarm sounds, the more time the dog has to realize he should turn around to avoid being shocked.
Change the metal prongs on the receiver. Most receivers come with two sets of prongs: short prongs for short-haired dogs, and long prongs for dogs with long or thick fur. Be sure the prongs are touching the dog's neck. Use the long prongs if your dog is not being shocked when he runs past the invisible fence. Thick or long fur might be impeding the receiver from working properly.