Another option besides putting in deep holes is to pour concrete into much shallower but wider holes, which can be done underwater (there are posts floating around here how to do that). Not sure how that will work in a filled pond though.

At this point after a few years, I would prefer a floating dock with a solid platform on-shore, and a pier that is allowed to pivot out to the floating section. It would resolve two issues:
1. Water level changes over 2+ ft causing fixed dock to look ridiculous way up in the air.
2. Being able to drag the dock-on shore for servicing/painting, etc.