How do I prevent water from getting in my landscape spotlight extension cord
To answer your question, water getting into the ground terminal of your extension cord will not trip the GFCI. If water gets into that hole though, it will probably get into the hot or neutral slot and that will trip the GFCI. Get a light with a longer cord or use some of the power cords you see in stores at Christmas time (see below). most come with covers and although not meant for year round use, they usually are.