Repair-It

So while moving, I'm discovering old internal hard drives that I've kept. Suggestions/advice on how to properly and securely dispose of them?

Hammer. smash the control board and damage the disk. I am not sure if there are recycling options after that. I definitely recommend destroying first.

Various levels of secure erase
https://dban.org/

The control board doesn't store any of your data. It will be easier to dispose of (e-waste recycling) and less messy without shards of PCB laying around. Unless you have a hybrid drive with a built in SSD for caching, in which case running DBAN will wipe your data out of the cache as it writes various patterns to the underlying disk. That said, damaging the disks will prevent data from being removed from them in the traditional manner. You can run a drill through them or, like Bill said, smash them.

One thing to note, if you are disassembling the drive, save the magnets. You never know when a really strong rare-earth magnet will come in handy. They also hold anything you want to the fridge.

Ok, at this point, i'm not connecting these drives back onto a computer to erase. So, basically some sort of physical destruction/disposing is what i'm looking at/for. Figured I could always use the smash approach, just wasn't sure if there were other options out there.