your problem must not necessarily be one of mod_perl, because some browsers (firefox i.e.) send several main requests for the same content to the server, in order to get the contents as quick as possible and to start rendering as soon as possible.
one solution might lie in mod_evasive, but unfortunately it will treat any requests for media on the page as main requests and block most of them. i once tried my own luck with a connection handler, but failed: Apache2 Perl(Pre|Process) ConnectionHandler. if you really need a distinct and unique status flag you probably better rely on session objects.