At most 1 running copy

I'm looking for a fool-proof way to ensure that at most 1 copy per user
is running of a single Perl script.  This code is horribly ugly and
needs to be scheduled frequently via cron but occasionally may run for a
very long time.  I'd like to ensure that if a copy is already running,
another one doesn't start up.  I need to do this with very minimal
changes to the running code (as I said, it's ugly and already does a
very poor job of error handling).

Any ideas would be greatly appreciated.  The developer had this coded in
there, but it's not always working correctly:

my $My_Name = getlogin || (getpwuid($<))[0];
my $ProgName = 'ftphandler.pl';  # update if program name changes
# check to see if user is already running program
my $Running=`ps -ef|grep $My_Name | grep perl | grep -c $ProgName`;
chop($Running);
if ($Running > 2) {
#print "already running.\n";
unlink("$Tmplog");
exit;
}

It's not my code, but I get to be the lucky guy to fix it and I'm a
crappy Perl coder...

Thanks,
        .../Ed
-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts@xxxxxxxxxx
Member #1, Red Hat Community Ambassador Program