When you edit your Spark Page you can set it to Friends Only. This will limit viewing it to the people you have added as spark friends only.
You cannot private the comments you make on other people's blogs, non-private Spark Teams, or these message boards.
Yahoo/Google may take a few days to 'drop' finding your Spark Page after you hide it, but while it will still show up in a result, if you are not logged into Spark, you would not see the page when you click the link.
Deb, in New Zealand