I don't think you have ever tried to get anything back from a habituated bear. You just have to consider it a total loss and pick up after the bear.Once they get teeth in and have a taste, it's all over. Canisters can't be picked up or bitten, so they lack the same level of investment for the bear. You can drive them off canisters.

Observe:
http://giantdumpster.wordpress.com/tag/ursack-failure/

No "properly tied knot" would have prevented that. In fact, the knot didn't fail.
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