Ok, firstly i'd incorporate a safe bot list where you can add bots that you dont want to be banned. The difference with this and .htaccess is, with .htaccess the bots don't even get to call any page on your site but having a lot in your .htaccess list can cause your server to load and slow down, this mod allows the call of a page...etc but as soon as they do it never completes for them as they are then redirected straight away and as you've experienced they quickly drop off and so does your server load

and you save tons of bandwidth.