use strict;
use warnings;

package MyTied;
sub TIESCALAR {
  my ($class,$code) = @_;
  bless $code, $class;
}

sub FETCH {
  my $self = shift;
print "Untie\n";
  $self->();
}

package main;
my $var;
tie $var, 'MyTied', sub { untie $var; 4 };
print "One\n";
print "$var\n";
print "Two\n";
print "$var\n";
print "Three\n";
print "$var\n";

OUTPUT:
One
Untie
4
Two
4
Three
4