That I tend to wrap my power cord in a loose loop over the cleat nearest where the cord will droop to the boat.

The mooring line is of course set tight to the boat, and I make sure the power cord has plenty of loose droop to the boat. But I don't want the power cord in the water, so I secure one end with a velcro wrap, and give the other end a loose loop around the cleat.

I always make sure that the cord will never be loaded by any movement of the boat, but at the same time, I don't want the cord in the water.