I didn't ask for a solution however there are far better examples of train proof mobs than adding such a terrible loot mechanic. Some ideas:
making certain mobs resistant to sleep would do quite a bit, as would not have teleporters that despawned all the mobs, mobs that have high enough damage ranged attacks, and placing more mini bosses or switches or other things which would take time in one place making training a less attractive option.
Really just about anything would be better than a dynamis like currency system or .001% super rare drop table.
