Thurs (Kiplward@gmail.com) asked a good question concerning the story of Fenrir recently, asking for “qualification” of the story. Specifically that particular version of the story was told to me by my grandmother when I was very young. This was her way of explaining to me why “wolves howl at the moon”.
When I got older, I did my own research into the Fenrisulfr and found the differences between the two stories. While not drastically different, there were some minor divergences from the “classic” myth told by Snori Sturluson. In Kevin Crossly-Holland’s book called “The Norse Myths”, he depicts the tale of Fenrir in Myth #7 based off of Snori Sturluson’s works.
One major difference in my grandmothers tale and the tale told by Snori is that Fenrir is not bound to the moon in the end, he is bound deep within the earth by a chain attached to Gleipnir named Gelgja that is thus attached to a giant boulder called Gjoll. The boulder is thus drove into the earth a mile underground and another boulder named Thviti is dropped on top of Gjoll. My grandmother included the names of the chains and stones in her tale as well, however it was not within the earth, but on the moon.

If you need more information on Fenrisulfr I would suggest looking him up online as there are hundreds, if not more, of resources available. Bellow are a few links.

Wikipedia entry (NOT A BAD STARTING POINT)

http://en.wikipedia.org/wiki/Fenrir

Encyclopedia Mythica (GOOD RESOURCE FOR BASIC INFO)

http://www.pantheon.org/articles/f/fenrir.html