I would still put the barrell up a tree as well. The bears will smell food inside.
Basically, you want to get your food high enough that the smell of your food is carried far away from it's location and/or dissipates before hitting the ground. About 25-30 is the height I hang my food/cooler.
(I am knocking on wood right now) I have never seen a bear while camping. I attribute this to being careful with ANYTHING that smells like food, including toothpaste, deodarant, etc. I also like to bang a pot just before I start cooking fish, bacon or something really fragrant.
Camping on islands or points will reduce your chance of bear encounters.