NIS with local root

We have a server sharing home directory trough NFS and NIS to user's PCs. On each client there is a local root for the user (these stations are used for system administration courses).
There is a way that prevent the local root to su to a NIS user, and so modify anyone personnal data ?
I think that there is no way to achieve this, but I would want to know your opinion.

Thanks in advance.

PS: please, excuse my english.

-- 
Nicolas Justin  -