If you build a fixed dock choose your materials carefully.
Neighbor guy did that in 2007. He used PT lumber from the box store lumberyard.
His dock is already falling apart. Literally falling apart.

I built a 12x16 floater with 4x16 ramp for my pond. It's pinned with 2.5" chain link fence post pipe.
It stays put just fine, and it's always the same distance from the deck to the water.