Take out the hard drive, open it up and remove the platter(s) - if more than one platter dispose of them separately, or if only one platter a propane torch might be handy. The circuit boards can still be recycled - and are what has most of the heavy metals.

I had a couple of old 40MB drives and this is what I've done with them. The platters were pretty thick and couldn't be bent up by hand.

Of course the likelihood of someone caring enough about the data on a random HDD to get it working again is slim...