Yes I have considered it, I dont think it would be better than straight out of the free flowing well. The pond is only about 5 feel deep and ponds has silk build up on there bottoms. I dont think I would get as good of heat exchange from the pond as I would from the well water. Plus people fishing would be catching the tubbing all the time. Im not sure what kinda exchanger the factory geo water source heat pump has, as far as plugging. I dont think there would be a problem using the well water using a tube to tube or tube in shell with removable clean out cover. I was thinking alone the line of building one like this
Sentry Equip | Tube-in-Tube Heat Exchanger