I realize that secure delete does not work with SSD's. However, I have external network drives that are normal platters and need to secure erase files on those. Right now, I'm booting Win 10 in parallels and using PGP (PGP doesn't work on El Cap).
Secure delete was removed in El Capitan as it caused confusion with those who had SSDs in their Macs. I'm not sure if there is a way to restore that functionality, however.