> even if poisoning people was ethical, how would the poison last 10,000 years?
Leave a fraction of the radioactive unshielded and buried less deeply, to ensure that wannabe grave-robbers die of radiation poisoning before they uncover much of the cache?
Nobody is going to die from radiation poisoning off the 10,000-year water unless they ingest it, and the hot stuff will be too cool in a couple hundred years at most.
"Toxic for 10,000 years" does not mean "get radiation exposure for standing next to unshielded waste", not does "cool" mean "non-toxic". The ionizing radiation danger of materials is inversely proportional to their half-life. Stuff that requires inches of lead generally has half-lives in the years or tens of years. Stuff with half-lives in the thousands of years can generally be "shielded" by a thick glass jar.
