If you want to create a subroutine that only the Foo package can access, lexically scoped coderefs are the way to go. However, I can only think of a few situations where you really need to be that secretive.

I find that most of the time all I need is to prevent a subclass overriding the subroutine, in which case I would either calling it as a subroutine rather than a method, or specify the package of the method directly. For example:

package Foo;

sub _init { shift->{foo} = 1 }

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    _init($self);
    $self;
}

package Bar;
use base qw(Foo);

sub _init { shift->{bar} = 2 }

sub new {
    my $class = shift;
    my $self = $class->SUPER::new;
    _init($self);
    $self;
}
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or

package Foo;

sub _init { shift->{foo} = 1 }

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    $self->Foo::_init;
    $self;
}

package Bar;
use base qw(Foo);

sub _init { shift->{bar} = 2 }

sub new {
    my $class = shift;
    my $self = $class->SUPER::new;
    $self->Bar::_init;
    $self;
}
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gives us

package main;
use Data::Dumper;
print Dumper(Bar->new);

__END__
$VAR1 = bless( {
                 'bar' => 2,
                 'foo' => 1
               }, 'Bar' );
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