This is why I structure any sizable program like this:

#
# Load global modules and constant data here
# 

sub foo { . . . }

sub bar { . . . }


{
    # Main code block
}
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Nothing of real consequence will run until that main code block, and that block keeps variables strictly scoped. On occasion, I need some static data for a specific subroutine, which I create like this:

{
    my %hash = ( bar => 1 );
    sub foo { . . . }
}
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This structure guarentees that the hash will be filled and in scope, without having to resort to BEGIN tricks.