Pet containment systems such as electronic fences do not prevent dog bites as well as ordinary fences. Dogs get excited and run through the boundaries. Neighborhood children are particularly at risk because the electrical systems do not prevent the kids from approaching the dog, and mislead kids because of the dog's apparent good behavior (which in fact was caused by the electronic fence).
Consider the following E-mail message:
My daughter was bitten on the face by a neighbors dog that was contained by an electronic fence in the front yard while the occupant was inside the house. She was walking up the driveway with my other daughter to ring the doorbell and see if their friend could come out and play. This bite will most likely require plastic surgery and already has caused an incredible amount of pain for my daughter.