A shot-gun and toss it into the burn-hole.I've taken 100s of hard drives apart (most need a T9 bit.....),remove the magnets (dang POWERFUL !) then use a 'bulk tape eraser' on the platters. There is NO way anyone can retrieve the data....it's all gone,forever.
The quicker method... secure HD in a vice, drill 1,2,3 or more 1/4" drills thought the platters. One is enough but 3, 120* apart looks neat !