OO - best way to have protected methods

[gargle]

I often use one of the following constructs for my private methods. Both have their benefits (the first gives a compile error, the second one dies during runtime but is easier to read). However, I wonder if there are other, better ways?

# private method add
my $add = sub {
        my $self = shift;
        my $amount = shift;
        $self->balance($self->balance+$amount);
};

or

# private method padd
sub padd {
        my $self = shift;
        my $amount = shift;
        caller(0) eq __PACKAGE__ || die "private method";
        print caller(0) . " " . __PACKAGE__;
        $self->balance($self->balance+$amount);
}