[CentOS] Shutdown hangs on "Unmounting NFS filesystems"

Once the system gets into this state, the only remedy is a forced
power-off.  What seems to be happening is that an NFS filesystem that
auto-mounted over a WiFi connection cannot be unmounted because the
WiFi connection is enabled only for my login and gets torn down when
my UID is logged off.

Any suggestions on how I can configure things to avoid this?  I
really don't want to expose my WPA2 key by making the connection
available to all users.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.