@RussellSawyer I don't use one but you should hang it because bears will destroy your food if they get hold of the sack even if they can't actually get into it.   There have been cases of this or so I understand.

Here are the why you can't use them in Yosemite...I assume this is still current...

http://cdn.ca9.uscourts.gov/datastore/opinions/2011/05/09/09-17152.pdf

That said this article seems pretty thorough on the subject of how to use them...I'm not endorsing it necessarily.  Just pointing it out the information...

https://www.youradventurecoach.com/ursack-bear-proof-bag/