I'm taking my 2010 iMac in for SSD installation. What is best way to secure my iMac? I have a mid-2010 iMac running High Sierra and I'm taking it to a local shop to get my fusion drive replaced with an SSD. I of course have sensitive info in the Notes App and elsewhere on my computer. What is the best way to ensure the security of my iMac? Is there any way of doing so without deleting everything?
Everything is going to get deleted anyway. Replacing one of the drives in the Fusion pair will render both parts unusable and very difficult to recover data from.
Assuming you've got a backup, which you will use to restore your data onto the new SSD, then you will lose nothing by erasing the Fusion devices.
Normally, the best practice for securing sensitive data is to encrypt the volume, but there's no point in this instance, as it takes time and is quite stressful for an elderly mechanical drive.