Posts : 3595
Maybe towers built in the field unattached to the castle can become unowned if they are not enterred by the original owner after X# of turns. 
TR
Posts : 424
interesting suggestion..however if you buitl a tower would you not have a key for the door.
Posts : 3595
Well maybe he left open the door
and by coincidence he lost the key also.
TR
Posts : 171
Not to mention pickpockets...
Oops, I mentioned them.