adams-mbp:etc adam$ ls -l /etc/hosts
-rw-r--r-- 1 root wheel 235 30 Nov 18:07 /etc/hosts
so unless you use sudo you can't update it. If you create a user that is not an administrator then unless you add the user to /etc/sudoers then you will not be able to use sudo and will not be able to update it.
You could set the system immutable flag. While the flag is set, not even root can modify the file. That would require someone with using sudo to turn off that flag first before it could be modified. It would at least be an extra step that's not very common.