Several years ago The Man Next Door and I tried to think of a way to keep our dumpster closed so the bears couldn't get in. Smart as they are, they weren't reading and heeding the Bears, Keep Out signs. MND finally came up with a really good solution. All he did was add a carabiner to the chain on the dumpster and voila! No more bear invasions. Except:
See how far open the dumpster is? This is when the carabiner is on the first link of the chain. Guess what? If the dumpster can be opened this far, small bears can get inside. I watched from my living room window last night as a small bear struggled to extricate himself from the dumpster. He finally made it - phew! I was worried though. He could have avoided getting in and the trauma of trying to get out, however, if someone had only left the carabiner on the fifth link of the chain where it normally stays.
See the difference? If the dumpster opens only this much, yes, the bear might reach a paw in and pull out garbage if the dumpster is really full, but the whole bear cannot and will not make it inside. And the Mama Susan won't lose sleep in the middle of the night watching and worrying over the process.