The recommendation from perlman:perltoot always seemed reasonable to me:

       But more often than not, you just want to make your class
       data a file-scoped lexical.  To do so, simply put this at
       the top of the file:

           my $Census = 0;

       Even though the scope of a my() normally expires when the
       block in which it was declared is done (in this case the
       whole file being required or used), Perl's deep binding of
       lexical variables guarantees that the variable will not be
       deallocated, remaining accessible to functions declared
       within that scope.  This doesn't work with global
       variables given temporary values via local(), though.

YuckFoo