Google "Bear bag hanging" and you'll get all kinds of ideas. I have bears around my house and they will get most items hung up if there is food in it. I've hung bird feeds way up in a tree and off on a small branch. They just climb up the tree, broke the branch off and had dinner back on the ground. I still have the claw marks on our tree as a reminder.
The best method is a rope hung between 2 trees, up 10-12 ft, with the food bag in the middle about 10-12ft from each tree. I never do this, I just hang from a branch high up (12 ft) that I can throw the rope bag (with a rock inside for weight) over. Takes me a few throws :-) The biggest issue I've had are racoons, squirrels, and chipmunks. These buggers show up with you just sitting there and make off with your food.