How to respond to attack on web site

How to respond to attack on web site

I have wordpress site that is under some kind of bot attack. I checked apache logs and there's get request to a single post on my blog every second (sometimes there's more than one per second). When i block ip address of attacker in htaccess file, requests continue but it's one every 5-10 seconds. If i unblock it, after few minutes it get's back to 1 or more every second.
IP Address of attacker is changing once or twice every day.
I have wordfence plugin installed that blocks attacks, i also manualy add ip adresses to htaccess, but i'm interested if there's another way to block this guy for good...
He's always identified as blank user agent, always get same page and it's always only one single page request.
Here's part of apache log with attack.
178.222.186.246 - - [20/May/2013:02:35:46 -0500] "GET /2012/01/19/skembici-u-saftu/ HTTP/1.1" 200 48097 "-" "-"
178.222.186.246 - - [20/May/2013:02:35:55 -0500] "GET /2012/01/19/skembici-u-saftu/ HTTP/1.1" 200 47939 "-" "-"
178.222.186.246 - - [20/May/2013:02:35:59 -0500] "GET /2012/01/19/skembici-u-saftu/ HTTP/1.1" 200 47970 "-" "-"