We believe that safety for you and your puppy should begin as soon as possible. That is why we created the Growing Puppy Program. Purchase a Big Dog Seat Belt at Regular Price… If your Growing Dog grows an additional 4-5 inches in body length we recommend replacing your seat belt with a new one. Big Dog will Custom Build a new seat belt at a reduced price of $69. We ask that you donate your old seat belt in good condition to a rescue or shelter near you.