Oh, I fogot to include something that also might help.
Top yudansha and potential successors might be encouraged to sign contracts outlining what they can and cannot do if they decide to leave. Non compete clauses are frequently used in businesses when hiring some employees. I don't know how that would work in aikido organizations, but its a thought. For example, a non-compete clause might prevent someone from opening a business doing aikido within a certain radius of the dojo they were training at. I guess you'd have to check the legality of doing this in a dojo where people pay membership dues-but it is a business.