trophy operated defensive structure
why not introduce a new defensive structure that only works when you have a specific number of trophies.
For example, The ice tower (suggested already in the sticky) which slows down the enemies only work when you are in the crystal league and above. When you get demoted the tower goes offline like the xbow without an elixir
*This will encourage players to work for their trophies rather than slacking in a lower league for the level you have.* EDIT to
This will encourage players to move up their trophy level and maintain it rather than just having the trophy level for bragging rights