Any xfconf property or channel can be locked down to prevent
specific users or groups from making changes. See the
README.xfconf for the list of properties xfdesktop supports.
Additional kiosk information is available at:
http://docs.xfce.org/xfce/xfconf/start
http://git.xfce.org/xfce/xfconf/tree/docs/spec/perchannel-xml.txt
