If you change your /home directory to be an NFS mount instead, you can use the root_squash option to have the root user on the local box map to an anonymous user on the NFS server. This would prevent root on your box from being able to modify the files in /home.
However, while root can never modify other user's files on the NFS server, beware that there are malicious things that root could still do. For example root could unmount /home and replace it with a seemingly duplicate /home that it could write to. It could also mount a fake filesystem over the top of another user's home directory that it could also write to. While the original files would still be safe and untouched on the NFS server, your users won't know how to look for this trickery and you might run into whatever problem you were trying to avoid.