Ideas for how to store ongoing case notes for clinician reference (not as a part of the client's formal chart)?

Has anyone identified a way to keep ongoing case notes (NOT the formal note we enter into their chart/sign on SP) that are for personal reference only (e.g. Remember to ask client about xyz belief; check in with client about abc event)? I am looking for a secure way to store my ongoing notes about clients that is NOT a part of their formal clinical chart (but can be stored securely and accessed through SP for my own reference). How do other people go about this? Simple Practice, do you have a feature for this that you could enlighten me on? Thanks so much!!