thanks for the reply.
So the point is we just set the permission of the file in which only the root have access. What I mean is that when the client mounts the exported fs, certain files/folders would be totally invisible to him.
ex:
/etc/exports
/mnt/nfs *(rw,root_squash,secure,sync,no_wdelay)

-bash-3.00# mkdir test
-bash-3.00# chmod 0700 test
-bash-3.00# chown root:root test
-bash-3.00# ls -l
total 1
drwx------ 2 root root 1024 Apr 10 17:35 test

When the nfs client mounts it, he can still see the folder "test" but have no access. My problem is how this folder will become hidden to him.
I tried hiding this folder but the client may still able to see if he set his browser to show hidden files.