Problems with root on network clients

[Alex Pires de Camargo <acamargo@linux.ime.usp.br>]

	Hi!
	I administer a network with server and clients Debian based,
and would like to know if I can solve this problem.
	It's a little easy to an user open a PC, damage the batteries,
boot with floppy and login as root in a client. But one thing is
undesirable. He can do su - <users> and do many things on users
homes. The rootsquash options on nfs solve the problem when the
user is root, but as I explain, this is not sufficient.
	Is there anything I'm forgetting to make? On server I run
potato, nis (not nis+), nfs-kernel-server.
	Thanks,

				Alex.