Blurring Faces that are still but Also in Motion

I am reaching out to find a specific tutorial regarding the effects tool. My job requires me to redact (edit) individuals faces that are still but also moving. I have you tubed and tried all the instructions but cannot get the blur to stick with the person throughout the video. There are times when the person moves off screen and then reappears. This is a new program implimented and I am trying to become as effecient as possible. Any advice would be appreciated. Thank you.

[Title edited by mod]