This doesn't work the way it wants to. The only reason creatures with Gold counters on them have defender is because Aurification has a continuous ability saying they do. If Aurification were to leave play and you countered the "When Aurification leaves play, remove all gold counters from all creatures." trigger, those creatures would still not have defender. You may be able to have "All creatures in play gain defender. (This change does not last until end of turn.)
They just get the counters as a memory aid, like Sensei Golden-Tail's training counters. They aren't supposed to do anything on their own.
Does it have to say "in play"? Doesn't saying "creatures" as opposed to "creature cards" imply that it only affects "creatures in play"?