host file in android

As is currently stated (revision 4), the answer is No.

Your hosts file is located at /system/etc/hosts, in a filesystem of (probably) ext4. Since ext4 uses regular Unix permissions and Android does not support ACL, you have no chance to do so.

However, I don't think you really should protect it as it's protected by default, because /system is mounted as read-only by default. As long as you don't grant your root access to malicious apps, no one will delete your hosts file.

Moreover, there are alternative dirty approaches but I don't think they're much helpful so I'm not posting them here.