You can easily make sure your public knowledge base isn't crawlable by Google/Yahoo/Bing and other major search engines. By default, ALL INTERNAL Helpjuice knowledge bases are, of course, not even accessible by search engines, however public knowledge bases are.
To ensure your KB isn't crawlable by search engines, all you need to do, is, include this single line of code anywhere inside head tag in Customize -> Main Layout page:
<meta name="robots" content="noindex, nofollow">
Yes! It's simple as that. Your knowledge base will not be indexed by search engines! Of course, if you'd like to make it crawlable again, all you have to do, is remove the same line of code!