use an Infinate Improbability Drive to escape from the Inescapable Box.
use a massive nanobomb to convert the surrounding countryside and the cubicle into a grey mass.
employ a the friendly neighborhood necromancer to put down any resultant zombies.
build new fortress.
surround said new fortress with shields. use magical powers to turn fortress unoticable, which is better than invisable. surround fortress with an improbability field and destroy all copies of the improbability drive but mine. then send the fortress to randomly move around in the empty parts of the universe.
put hill in a small adament box. lock said box with an unpickable adament lock. i then keep the key in my impenetrable safety deposit box that can never be found by you puny mortals/immortals/undead/whatever.
put a flag on the box, emphasising my ownership of the hill. take a vacation & let you figure out how to open box or find the key. 
also, i steal your sandwich. it is very good, though i could use some cake...