This was figured out by Mtld
while we tried to get this achievement.How to lower your attack & defense
If no one is attacking you or if you have a fellow that wants to attack you but your units are to strong, try this:
1. Use up all your air AND ground units until you only have 1 of the weakest for each.
2. Sell all your unit buildings.
3. Build 2 watchtowers from the base category (this will give you another achievement)
4. Wait approx 1 day for the game to recalculate your stats
All of this is necessary and it works. People with 2.500 defense got down to 100.
If you need someone for attacks, you can send me a message.