Hello,
Well I never knew about this till now, and to be honest I think the best solution should be is to log the people that are constantly changing from peace to battle mode on x period of time, like on the old servers it used to log cast hack and stuff like that...
Now I don't know if the client send a request to the server to change the battle mode, and honestly I don't think so, so most likely in that case it will be hard to log whoever is doing it cause the server doesn't know what's going on...
Somewhere, somehow, it could be detected and like I said whoever is doing it should be banned.
There's my 2 cents.