In addition to the hugely anticipated solution and to completely stamp out the use of dummy accounts to gain ingame advantage on a main. I have a final solution.
Implement a system that removes the last 3 days of contribution of the player from a guild bank when the player leaves or is kicked. This would nullify any benefits of alting. I've not explored it in full or have specific suggestions to implement it however I would be happy to explore the idea further through discussion.