This stratagem should bear fruit, in theory. But their opponents...

     They are evil : during a war, they usually put some pieces of fire around the castle until it is only possible to walk there by knowing the position of them and avoiding them. Otherwise, the whole place really is a deadly trap. Please be careful. The trolls will ask you a lot of money for their work.

     However praiseworthy it may be, they seldom solve problems. At times, I believe it would be faster to call the police directly. But don't worry.