Lord Jimbob
Lord of the flies
I used a 'maginot line' sort of defense very succesfully in a recent game: all i did was build barricades along my land border one-deep w/no units manning them. my enemy comes over to attack, is forced to stop at the barricaded border, than i just moved in my artillery (keep 30-100 available depending on world size) and red-lined the invading units, followed by destruction with whatever unit i want, although i kill the final invader with a mobile unit (horseman/knight/cavalry/tank/bomber/hwacha etc...) so i don't have to leave a unit directly on the barricaded border, where it is exposed to enemy attack during the interturn. i don't have to spend labor building barricades 2-deep along my border, and i don't have to keep the border manned with defenders. caveat: you have to be able to kill all invading units on the turn on which they arrive so they don't attack your cities next turn...