Darkvillain :
The only REAL way to make it so no data can ever be recovered is to smash the hard drive. There are programs which can bring anything that once was on the drive, back onto the drive. So if you are worried about something being found on the drive, smash it and buy a new one.
Yes, but they are only available with organizations like NSA and experts of that caliber, who are usually not rampant.
But its a wise suggestion.
Goor read... https://www.powerdatarecovery.com/recover-deleted-files/recover-permanently-deleted-files.html