I have 3 giant breed dogs within no barking ordinance. its seriously difficult to control site hounds even behind 6ft privacy wooden fences. they are large enough to look over the top. I have bought very expensive brands from petsmart and other pet outlet stores. they pulled them off each other in play, played in the pond and destroyed them, plus they never stopped the barking. These work. THe first time I used them stopped it. altho I still have to play with the sensitivity a bit, my one dog shakes her head and the alarm warning goes off. they are also water proof! that has already been experienced. I am thoroughly satisfied with these models. My dogs necks are around 24 inches and these fit well with some room to spare. finally I don't have to chase after them to silence or scold them, these really do work and after first day, just wearing the collar even if its not on seems to remind them to cool the barking. try it!