I know I keep going back to a 55-gallon drum but the concrete also makes me think that because people used to/may still put things they want to get rid of in a drum, put in concrete to make it heavy, hammer the lid on, and dump the drum in water. Lots of environmental contamination used to go that way. Even soil would work to weigh it down. It’d be heavy to get up into a truck bed—banging would occur for sure as you rolled it in there. Also, and I hate to say this, but even in the country, you often can smell something like a deceased raccoon or deer if it’s out in the open, and surely people looked for buzzards right after. On the lye, etc., if a drum were found still sealed, I imagine a chemist could ascertain that something else had been there, too, based on the laws of mass and all that—or something!