lucy24 - 4:39 pm on Nov 13, 2012 (gmt 0)

Are you asking about robots visiting-- for whatever reason-- or about nonexistent pages getting indexed in search engines?

robots.txt would not do a speck of good. If the site uses no queries at all, it can be as simple as:

RewriteCond %{QUERY_STRING} .
RewriteRule .* - [F]

That is the minimalist version. More details may be necessary.