How can I password protect a meterpreter backdoor?

In metasploit unleashed the basics of using meterpreter as a backdoor are explained, including installing metsvc.

"One word of warning here before we go any further. Metsvc as shown here requires no authentication. This means that anyone that gains access to the port could access your back door! "

The above kind of indicates that there are methods to pass protect metsvc? If no, could someone please mention other backdoor methods that I can google about?

Thanks a bunch,