Find fishing bobber "owner" in Minecraft 1.16

I’m attempting to allow someone to use a fishing rod and essentially make an ore buster. I’m just not sure how I would be able to efficiently find the user of said fishing rod and perform the rest of the actions I need for the ore buster, without also letting it happen to other, normal fishing rods.

The following are different ways I’ve thought of, and reasons why they may not work and/or why I’ve had trouble with them;

1. Using the player’s SelectedItem to see if they’re holding a specific fishing rod, then test for fishing bobbers near them while it’s active. For one, SelectedItem has always been unclear, and the data values section for the Player on the wiki doesn’t tell you. It simply says "See Item Format" then sends you to a dead section.
2. Simply testing for a fishing bobber near the player. This is simple, but prevents people from using normal fishing rods as well.