our $Debug=0;

# lots of subs that work

sub doesnt_work_quite_right {
  local $Debug=1;
  
  # code that we are trying to debug
  
}

##</code><code>##

my $Debug;

sub doesnt_work_quite_right {
  my $olddebug=$Debug;
  $Debug=1;
  
  # code that we are trying to debug
  
  $Debug=$olddebug;  
}