I have an outdoor gfi receptacle for outdoor low voltage submersable lights for a fountain. It was installed initially about 6 years ago and has been replaced about 5 times. I have a code keeper cover so I can leave the transformer plugged in. It typically trips a few times over many months(although not initially) and then eventually won't reset at all. I replace it and the whole process starts over again. There is no evidence of water or moisture inside the box and this last time I replaced it with an "outdoor weather resistant" gfi but still got the same results. Any suggestions? Is my transformer causing the gfis to fail?