I didi the repair today. The original install was three circuits, each to a double gang weather box at the pond. They had put a gfci dead front in the box with a blank cover over it, then caulked the dickens out of it. This was ok until the gfci tripped. I was an easy fix. I put in use covers on the boxes.
I tried gfci breakers. That seemed to be the best set-up, however they wouldn't hold.
