Hard Drive destruction question?

[FoxtArt]

The outside circuitry might be harmed by saltwater, but it's unlikely any saltwater would get into the platters, where data is stored.

If you have the capability to burn a hole through it (oxy/acetaline comes to mind) that would work.

Smashing also would work. Which I know, you don't want to get messy. You could disassemble to get to the platters and then do whatever to physically damage those.

Shooting would work, but you really shouldn't shoot mild steel - ricochet risks.

Disclaimer: Now, there's specialized (partial) recovery that can be done even when platters are physically damaged, but it's not too likely someone's going to spend $5k on each of your landfill drives to do that. IMHO it's better to have a platter damaged along an entire axis (like a crack radiating out from the center-out) as opposed especially to a single hole, which could allow recovery in sectors of continuous tracks unaffected by the hole - even if it is unlikely and requires special equipment.