Decks, Patios, Porches and Docks - Support post base

I have just had a support base replaced because the builder put in a non-pressure treated post that eventually rotted through. My house is on a steep slope and the wrap deck is cantilevered over the hillside.

The post holds up a corner of the entryway porch of my house and extends about 2 feet below my deck to a concrete footing. Because there is a substantial amount of river rock trim, I'd like to finish the base of the support post with river rock I picked myself. The post is 9" X 9" and the rocks would sit on the deck.

My plan was to create the stone base with the larger rocks at the base sitting on the top of the deck and taper up about 1-2 feet with gradually smaller rocks. How do I mount them? I will eventually replace the decking w/a recycled product, so I need to find an attachment method that would enable me to eventually remove the deck boards.

Thanks!:coffee: