I think that you may use some Big Data folder in which you keep your high definition videos etc.
Just format the disc once and then copy this big folder, over and over again until it fills up the complete Hard Drive. This way all the tracks of your old data will get covered up with this new data.
If you want even more safety, then you can repeat this complete process once more. After that I do not think there is any chance left for recovering the original data that you had on this hard drive.
If I am wrong in this assumption, then please correct me.
Thanks