Final answer:
The use of a degaussing tool is the most secure method, short of physical destruction, for ensuring data on a hard drive cannot be recovered.
Step-by-step explanation:
When it comes to ensuring that data on a hard drive cannot be recovered, the most secure method, aside from physical destruction, would be to use a degaussing tool. Degaussing effectively disrupts the magnetic field of the hard drive, thus making the data unrecoverable. Formatting the drive or repartitioning it simply alters the file system in such a way that data appears to be deleted, but can still potentially be recovered with specialized software. An overwrite program can provide a high level of security by writing meaningless data over the existing data multiple times, rendering it very difficult to recover the original data, but it is not quite as secure as degaussing.