Lupo Professional Ultrasonic Dog Training Whistle with Lanyard, Adjustable Frequencies & Free Training Ebook Guide GUARANTEED BARK STOPPER train your dog to stop barking, follow commands and become obedient with the bark stopper whistle and our FREE Ebook guide EASY TO USE AND COMPACT the LUPO Dog Whistle is light and compact. The perfect bark stopping deterrent. ADJUSTABLE FREQUENCY find the perfect frequency for your dog.