how to stop admin-user changing file permissions
 

Problem was to allow teachers to access pupil home-dirs. Achieved this by putting admin users = staff, but that creates a problem in that if a staff member opens and saves a word doc in a pupils home dir then the file permission for "user" are changed to root and the pupil cannot write to their own document again.
Tried setting suid on pupils home dir but this does not work when admin user is used.

Any suggestions.

The other solution to the original problem was to use acl's (I think) but these have not been installed on our unbuntu samba server and some linux users express need for great caution (i.w. try it out on spare partition (which dont have) first. so pefer to find another solution if possible.

you need to set sgid to the directory