I have read that the most secure way to erase a MacBook Pro's SSD before selling is to encrypt it first using File Vault and then erase using Disk Utility. However, I have already erased the SSD using Disk Utility and I was NOT using File Vault to previously encrypt the drive. What can I do now to make sure all of my information is not retrievable by anyone buying the computer? Can I encrypt the empty drive now and then erase again? Would this also encrypt and securely erase any previously deleted remaining/retrievable data?