usually using FD and a tribute will keep the AI away, though the richer the faction the higher the tribute i usually have to use. Keeping your bordering garrisons a bit higher will help considerably along with causing revolts and wars between the AI (using assassins and spys). It was a key in my survival as saba against the yellow death.

Also in my romani campaign i couldnt get the aeudi to accept a ceacefire, so i campaigned through their territory's and took everything but 1 city burning and enslaving all of them and then giving the bordering towns to my allies the Averni. Had to FD the settlements to my allies, they wouldnt accept them (youd think theyd be happy i just ended the civil war and made them the winner).

Figures their currently being eaten by the swezboz.