You can't. The source is necessary for the browser to
display your document. You have to send the complete,
unencrypted source to the browser. Even if a particular
browser doesn't have a "View source" option, there are many
that do, and you can always retrieve the document by hand
(using telnet) to get its source. Or check the browser's cache.

You can of course put a few hundred empty lines above the
actual source, then newbies who don't see the scrollbars
will think there is nothing there.