What if a canister gets stuck in a hole?
If there are unexpected challenges with retrieving an object, then there are specialist companies that can “fish” for uncooperative objects such as a broken pipe. They regard retrieval of a canister, something that is “cooperative” (has structures purposefully built-in to make connection easier), as straightforward. We are in the process of conducting our own tests to ensure retrieval of our canisters could be accomplished in the same manner.
If for some reason, retrieval and fishing fail, then no further waste will be placed in the hole and the hole can be monitored, and eventually sealed.