Hidden Fences: General FAQs - Drs. Foster and SmithHidden fences are electronic pet containment systems (also called "underground fences"). These effective systems create an electronic ... Properly fitted, the collar should be snug, allowing enough room for one of your fingers to fit between your dog's neck and the collar. The size and weight of the receiver normally ... However, it should not be submerged in water, as this may reduce the battery life and cause internal damage to the components. Waterproof means the component is ...