Get a gun and shoot a few holes in it, drill holes in it, and whack it with a hammer for the best result
First, you will want to drill holes in the platters on the drive, then you will want to hot it with a hammer, then shoot the drive
I recommend a .12 gauge shotgun for this, as this produces a really large hole in the case and platters, and doing this a few times in different areas of the drive will easily prevent recovery
If you need access to a gun and don't have one, ask to go to the shooting range with a friend and shoot it, and get access to a gun in some way you can, should you opt for this method
A word of warning about using a gun: THEY ARE NOT TOYS! YOU NEED TO HAVE SUPERVISION IF YOU ARE NOT 18, OR HAVE A GUN PERMIT, OR UNFAMILIAR WITH GUNS! I REPEAT, GUNS ARE DANGEROUS IF YOU ARE NOT CAREFUL!
Here is a video on the 12 gauge slug thru a harddrive(this guy has the right idea where to shoot it), but shoot it more then him
Because I DID bring up the use of guns, I have to bring up some obligatory safety warnings
Do this in a shooting range if you possibly can(if you have lots of acres, I suppose that would work, but make LOTS OF room for the slug to land in a somewhat predictable spot), go with a shooting range tough as it's preferred if you can go to one that will allow you to shoot something like this
WEAR SAFETY GLASSES!
Keep who is watching behind you at ALL times and make sure they have safety glasses and hearing protection, if they come with you and watch
Make sure there is PLENTY of room for the slug to land so nothing is hit, or there is a slim to none chance of it happening
GUNS ARE NOT TOYS! YOU NEED TO HAVE SUPERVISION IF YOU ARE NOT 18 OR HAVE A GUN PERMIT, OR UNFAMILIAR WITH GUNS! I REPEAT, GUNS ARE DANGEROUS IF YOU ARE NOT CAREFUL!
Again, I cannot stress safety enough, follow my tips and warnings all over this post, they are all for your own good
I know some people know this, but some people don't know, so I had to put this in too
The non gun method
Being not everyone will agree with my other idea to destroy a hard drive, i will give a way to do it, and get similar results as the above method if my other method isn't to your liking
Get the largest drillbit you can get, and drill at least 6 holes in the platters evenly spread out, and make sure it goes all the way through, you can check by removing the drillbit or going through the back of the drive
Drill a hole in the IC's on the drive's controller board too
Hit the platters with a hammer enough to dent them deep, and put lots of little nicks in them too