I sent it back, not because it does not work. let me explain. I have a mastiff. i measured her and it should have been snug according to measuring her and the product. however it was past snug. I looked all over the internet as to how this could be. essentially you need about 2 inches more than whatever size you are buying, so for example if her neck is 23 inches, she needs a 25 inch collar. I thought, well ok, i will buy one or two individual prongs then, but this company didn't offer it so i sSee full review