What about making it so that if you leave the County Capital you can't come back at all?
I mean, think about it ... for those that join, they are interested in joining because they want to retire from dueling, or they have completely built up their own town, or they don't want to be dueled and have not joined a town because they could be ... what would be the advantages to them for leaving? They'd be losing out on all of the "privileges" of being a member of the County Capital and they'd not be able to rejoin. This would completely remove the "hit and run" duelers from the equation.
And those that joined the CC because they have built up their own town as far as they could aren't likely to leave the capital that they can build to infinite levels to start another town they know can only go to a certain level, so why would they want to leave?
Leaving the CC doesn't make any sense other than for the "hit and run" duelers, so if you join and then leave, you shouldn't have the option of rejoining.
Or that if you are kicked, you have to be "voted" back in by the current members of the town (if there is an available space) based on your previous contributions to the Capital. (For example, BartBot is a member of the capital for 29 days, has kept up on his "taxes" and has done everything necessary to ensure the success of the capital, but got into an accident that required him to be away from his computer for several weeks. He's kicked for failing to pay his taxes or contributing to the town for those several weeks. He can reapply for membership -provided there is space- and the members of the town can look at his previous contributions and make the decision that way -in this case likely in his favor due to his absence being beyond his control and his previously exemplary behavior)
Also, there would need to be some kind of checks and balances for those within the CC for "paying taxes". For example, if you set the tax at 1% of their weekly income, then you risk the chances that someone is not going to work very much so that they don't have to pay much in taxes, or for builders to not go out and earn money by using the excuse that they are "building up the capital" instead.
I would think that a set amount, for instance, $500 a week (a week being 7 days) would be the way to go, because then if a player hasn't contributed that much, they can be "let go" from the Capital to make room for someone else who is willing to "play by the rules".
Also, builders might get a "bonus" and be required to pay slightly less taxes in return for a certain number of hours being spent on building up the capital. For instance, instead of the $500 tax they pay $300 per week but have to spend at least 10 hours working on building up the Capital. (This could be a sliding option allowing for them to choose from week to week which option would be better for them, but they would need to meet the requirements of one or the other to remain in the capital).
Also, by setting a definitive tax, it would remove from the Capital those only wishing to join so that they can go on vacation or be absent for some other reason for an extended period of time but yet maintain the benefits of being in the capital (being in a town with a bank and not being dueled).
I think this idea is a spectacular one, and if all of the details can be worked out, I think it's going to be a fantastic new addition to the game.