Shut the power off, pull all electrical equipment and thoroughly check every cord, plug and where the cord enters the device. If there's any sign of wear, exposure, etc., replace the equipment. Do not tape it up or try to repair it. It's not worth it. Someone can literally die.
If your pond is not protected by a GFCI, then you need to correct that.
And yes, GFCI's can and often do go bad.
They can be in outlet (receptacle) form which will protect anything plugged into it or anything hardwired off of the load side of the receptacle.
The circuit breaker type protects everything on that circuit.
You can get a short extension cord type GFCI that you can use for plugging in your power tools when working outside, but that's just temporary and not meant for permanent use.
You shouldn't be plugging into or connecting one GFCI to another GFCI.
All GFCI's have test buttons. Manufacturers usually state they should be tested monthly.
All your outdoor cords should be three prong. Third prong being the grounding conductor. Make sure the third prong hasn't broken off.
Extension cords are not meant for permanent outdoor use. Install the proper weatherproof conduit and boxes and covers. If you're using an extension cord temporarily, it may seem like a good idea to wrap electrical tape around the plug connections, but that will usually just trap moisture within the tape. Just leave off the tape and arrange it so the prongs of the male side are facing up. If the female side is facing up, water will accumulate in the slots.
All outlets whether indoor or outdoor should be three prong and properly grounded.
Never pull your pump out of the water by it's cord. Tie a string or thin rope to the body of the pump for easy retrieval.
