How to prevent bots to enter specific pages on my site by a capture
It sounds like you want to guard against robots that ignore robots.txt. Or possibly against spambots that are trying to exploit your comments section. I think the easiest way is to not allow anonymous users access to the page. Then, if you protect the login page with captcha, you should be able to keep any bots where you want them.

You will need the Content Access module and the Captcha module.