Monitor CIFS mount on Linux client?

We have Windows shares mounted as CIFS filesystems on RHEL5 servers
running Oracle DBMS, e.g.
# df -P|grep -E -e cifs -e Filesystem
Filesystem         1024-blocks      Used Available Capacity Mounted on
//windows.nowhere.com/oracle 1098613024 887737788 210875236      81%
/windows.cifsxport

These become non-functional somewhat randomly on individual servers, which
we usually find out about when the Linux box goes purple because the "df"
for the disk test has hung.

I can exclude CIFS using df options to avoid the hang, but then I won't
get any warning at all unless I find a better way to check the mounts. 
Suggestions?