As a root user, you can lock all user's websites (mysql databases and files) in read-only mode so they can not be modified!
Files
To block all changes on files:
sudo chattr -R +i /home/USERNAME/docker-data/volumes/USERNAME_html_data/_data/
To undo:
sudo chattr -R -i /home/USERNAME/docker-data/volumes/USERNAME_html_data/_data/
MySQL
To block writting to all user's MySQL databases:
in /home/USERNAME/my.cnf add:
read_only=1
super_read_only=1
and restart mysql/mariadb service for user: docker --context=USERNAME restart mysql
To undo, remove those lines from the file and restart user service.