Because of their nature, there is no real need for the usual fencing methods to keep them in place. What works best is loud noises and lots of vibration, which is why railway lines have so many bridges to cross, or go under. The trolls hear a train coming, feel the vibrations and then dive for cover, fearing it is Thor out hunting them.
The cache is a Bison tube, please bring something to sign the log.
Congratulations to The Hartshorns on being FTF, well done.