The standard ways of protecting files include hiding them and encryption. Of course, both of those would interfere with the function of the Hosts file.
You might be able to hide the file (write-protecting it won't help or matter either way) and disallowing said user access to the option to "show hidden files".
Other than that, without third-party software, you're out of luck.
You might be able to hide the file (write-protecting it won't help or matter either way) and disallowing said user access to the option to "show hidden files".
Other than that, without third-party software, you're out of luck.