in: robots.txt
User-agent: dotbot
Disallow: /
Alternatively you can explicitly disallow all disallowed pages:
User-agent: *
Disallow: /~joe/junk.html
Disallow: /~joe/foo.html
Disallow: /~joe/bar.html
User-agent: *
Disallow: /cgi-bin/
Disallow: /tmp/
Disallow: /~joe/
User-agent: Google
Disallow: