I'd be seriously thinking about a return line off the regulator like Pope said to bleed off some of that pressure when you shut the boat off. A fuel shut off is a good plan, too, but IMO it would work best to run the shut off in the line before the regulator, then at shut down close the fuel shutoff, let the engine run 5 to 10 seconds more to bleed off the pressure, then hit the kill switch. With all the heat, plus the heat sink off the engine, the fuel is going to be expanding a lot after shut down and probably flooding the engine..... We've used the shutoff valve and return line method for years on drag and circle track engines. No reason it won't help out a boat, too!