To secure erase when that option isn't available in Disk Utility. For example, for SSDs. Boot from another disk or recovery mode. Erase the disk encrypted, with a complex key. Fill the disk with zeros. Erase it again, without encryption or with a different key.
Options to fill with zeros
If it is available, use mkfile, otherwise use dd...
I usually write a blog post about once a week. The latest post can be viewed here: Learning from Failure: I think there is a place for parties with views I find insane. (posted 2024-11-28 at 12:41:49). I do podcasts too!. You can listen to my latest podcast, here: OJB's Podcast 2024-08-22 Stirring Up Trouble: Let's just get every view out there and fairly debate them..