Is it possible to protect a game played over a modem from being hacked by an opponent using ArtMoney?

I apologize for the repeated topic – it was unintentional.
No, I calculated everything, literally, all the income, and calculated the cost of the army. Everything is accurate. It turns out that it's impossible. The difference between the army's cost and the income from all sources increases every month.
The question is, how to limit cheating, other than daily saves and "trusting people"?