Kobayashi posted the following a while back on CivFAn.

The Invinciple Pirate Port Idea
Its basically a variation of the sleeping beauty city (for those of you unfamiliar with my scenario building tip, its a city built in the ocean where all units fall asleep as soon as they are built). Just had this fantastic idea to combine it with barbarian ownership (I have already tried it out and it works) 
1. Create a settler for race A and then use it to build a port city on a grassland tile. (not the event create unit, use the cheat menu) 
2. Edit the city to change its size to say 5 
3. Set reveal map to barbarian. 
4. Create a few barbarian warriors next to the city 
5. Set player to none and hit return. 
6. The barbarians will takeover the city and start producing warriors. 
7. Use the terrain editor to make grassland change to ocean when you irrigate. 
8. create a race A setler inside the barbarian city. 
9. Activate the settler and close the city screen. 
10. Order it to irrigate. 
11. Disband the settler. 
12. Reverse the terrain change so irrigation becomes normal again. 
13. Use the unit editor to change warrior to some kind of ship 
(The concept should be novel because not many people would know all the bizzare techniques I've listed let alone combine them in this sequence. However, if someone else has thought of this before, do let me know.) 
a. Ships won't fall asleep so they can go hunting as soon as they are built. The city will keep churning out pirate ships. 
b. Enemy ships and planes can attack but can't occupy the city. 
c. Enemy land units can't attack as the city is on an ocean tile. 
d. Probably the only way to takeover the city is to use helicopters. (not tested0
variations: 
If you change the city style of race A to invisible, make sure no other race has the same city style and then kill off race A, you can have pirate ships appearing out of nowhere. 
If you change the terrain of the surrounding land to ocean, you will have an invisible invincible pirate port which is almost impossible to find. This could also be a rift to another dimension which lets invaders in. 
You can create a special way of ending the pirate threat - a quest which will result in a change in the terrain of the pirate city tile which will then erase the city. 
You could also use the same concept on land if you changed the warrior unit to a plane with say 50 turns in the air.
[This message has been edited by kobayashi (edited August 06, 2001).]