I'd never trust one. I'd never leave a dog unsupervised outside with only electric fencing. Of course, I have huskies and occasionally 7 feet of high strength wire, buried a foot underground and reinforced with concrete hasn't been enough to keep them in the yard!

My other issue with them is they don't keep other animals out...loose dogs, roaming cats or where I live bears, moose, wolves, coyotes and foxes! My fence is built as much for keeping the area wildlife out of my yard as it is for keeping my dogs in the yard!

Daisy has an electric fence at her real home...Daisy who has been at my house pretty much daily for 8 years! The shock occasionally stops her from going home, it never even slows her down when she's leaving. I haven't seen her collar on for quite awhile; her owner probably gave up on it or my dogs chewed it off her again!