Another thing that works, especially if you're on an older server is stacking up your city to the rooftops with stone, which is probably at that stage practically worthless and chances are yoru attacker doesnt need it.
Buy 100m+ stone per city (should be fairly cheap). Since the attacker gets proportional percentage of all respources, even if he manages to get to punder you, it will take him a lot of runs to get anything worthwhile, buying you time and increasing the chance you'll keep enough food/lumber/iron. Might even keep soem of the 'big guys' away as you become more trouble than you're worth ;)

