Little bastard, challenge accepted!
This is the patented harness that prevents puppies or small adult dogs from escaping fenced-in areas. The device slips on a dog like a common harness, but its integrated rigid 10 1/2"-long cross-bar spans well beyond the width of the pet, preventing it from slipping out between fence railings. The lightweight harness won’t inhibit a dog’s movements and allows passage through most standard pet doors.
More info: Escape Preventing Dog Collar