Hey Guyus,
Just had another thought. i play the brutii allot and my strategy for the mainland is to get Greece and MAcedon fighting each other then take over. I imagine the AI might try to do the same thing. Get the Brutii into a war versus the Greeks and MAcedons at the same time and that ought to put a crink in their plans. If the Greeks and MAcedons ally versus the BRutii they will not be able to spare units to march north and will be bogged down in the peninsula indefinately.