To address this pond that is being installed on the outside.
The use of NM cable installed in a raceway on the outside of the house is addressed by 334.12 and 225.4.
In short NM cable can not be installed outside.
Under the 2005 cycle of the NEC there are two articles that will need to be looked at. 680 part V (Fountain. Fountains, ornamental pools, display pools, and reflection pools.) And 682 (Artificially Made Bodies of Water. Bodies of water that have been constructed or modified to fit some decorative…..)
Under the 2002 cycle 680 part V was used for the ornamental ponds that I installed in the area that I work in. I haven’t installed one under the 2005 cycle.
As to protecting the pump with GFCI, I would strongly recommend this. I have a Koi fish pond at home. I lost the first couple of fish due to a bad pump motor. The fish died due to electrocution.
Should the GFCI trip the fish can live for a few days without the water circulating but they won’t make it long with current flowing through the water.