lucy24 - 1:39 am on Feb 29, 2012 (gmt 0)
Some years back I 403'd blank UA's... I'm a half inch way from doing same for Referers (sic)
Compromise: block everything but your front page. Otherwise you're slamming the door on normal humans who started on some interior page and want to see what the overall site is about. It doesn't take a whole lot of know-how to manually delete everything in your browser's address bar after the domain name, and hit Return.
You could set a cookie saying they've been here before, but that's just a variation on the identical problem.