While you can drill your holes and hit it with a hammer and the damage will be sufficient, there's another option at your disposal: Shoot the hard drive.
Obligatory warning: This is option is DANGEROUS if you do not take the proper precautions. Take the drive to a large acre of land or a open shooting range to ensure you don't accidentally shoot anything (or anyone) around you and can contain the slugs safely. This can be a problem in areas with a moderate amount of foot traffic. If you're under 18, take the hard drive to the range and do this while you are under adult supervision.
The first thing you should do is drill your holes and smash the drive with a hammer. Once you do that and decide you want to inflict further damage, then I would go ahead and shoot the hard drive.
The key thing here is making sure the gun type and ammo gauge will do a good amount of damage to the drive. I'd suggest looking into a .12 gauge shotgun for this, since it will do a fair bit of damage to the drive.
I'm not going to get into how to obtain a gun to do this - you're absolutely on your own here.
Ideally, this is what the drive should look like when you are done: https://www.youtube.com/watch?v=6pZD99lT...
Obligatory gun safety advice:
- Guns are not toys. If you are not sure if it is loaded, assume that it is.
- Take the drive to a place with lots of open land or a shooting range.
- Wear eye protection.
- Make sure everyone around you knows to keep a safe distance from you.
- Make sure the slug can land somewhere it is not a risk to anyone in the area.
- Follow your local laws.
Gun safety should be your #1 thing if you actually decide to shoot the hard drive to make sure the data is beyond data recovery. If you know this that's great but I need to put it here just in case someone who has little time around guns sees this answer and decides to shoot their old hard drive before they dispose of it.
Destruction without shooting the drive
If you are not comfortable around guns or think that shooting the drive is extreme, you don't need to go that route to destroy the drive. If you would rather drill your holes and smash the casing, this is often sufficient for the average person disposing of an old hard drive.
It also doesn't hurt to destroy the PCB just to be sure that data recovery is not worth the effort. All you really need to do with the PCB is smash the chips and interface and this should be sufficient to make the PCB unusable.