You can ban bots that don't adhere to the robots.txt file by having a "secret" folder and file that is disallowed in robots.txt and not visible to normal web surfers (no links to it, etc.) Typically people put a no-index, no-follow header in it so it doesn't show up in search engines.
You then scan your logs for visits to that page, and ban the IPs that find it. Some programs have been written that provide the list of IPs ... see http://www.kloth.net...net/bottrap.php and http://danielwebb.us...tware/bot-trap/
You could hire someone to implement that kind of thing for you.
Thanks for the tip. Much appreciated. I'm waiting for a reply from a few people right now. Wish me luck.