I have a customer who is asking that I install a receptacle under the edge of his boat dock. He wants to be able to plug in the battery charger on his boat. He does not want to have a cord running across the walkway to a receptacle about 20 feet away. He wants to be able to have a short cord to a hidden receptacle under the edge of the walkway. I know it is not the ideal situation and would have to be GFI protected if legal. I know there a rules about receptacles around pools but this is the lake. I need to know if this would be a legal application or not. I would appreciate the help.