chmod - Shared hosting, stop user deleting .htm file?

Hi guys I have set up a small shared hosting set up for friends.

I have set the file chmod permissions to

chmod 711 /home
chmod 711 /home/testuser
chmod 755 /home/testuser/public_html
chmod o+r /home/testuser/public_html/index.htm

How do I stop the user connected to their own ftp from deleting the html.htm file and also with the public dir set to chmod 755 I find they can't do anything in the directory such as upload/delete?

Additional info: I have run

setsebool -P httpd_enable_homedirs true
chcon -R -t httpd_sys_content_t /home/testuser/public_html

but no effect?

Answer

You can make the file immutable, with:

# chattr +i filename

then even root user won't be able to delete it.