The LeadaHose dog leashes are designed for owners of dogs that love nothing better than splashing about in puddles and getting all muddy. They are integrated with water hoses that let you spray your dog down after it's done its muddy tomfoolery, or even just to cool it down in hot weather.
These leashes have a tap connection and a dog collar-securing clasp on one end, and a spray nozzle on the other end. So all you have to do is find a tap fitting, connect your lead to it and spray away at your muddy mutt.
The LeadaHose is currently seeking funds on Kickstarter. A minimum pledge of $25 will get you one in December if the product meets its fundraising target.