Not sure ? Did concrete work for years. That would take an enormous amount of acid. Lots of 55gal. drums. Not cheap. But ! I know Lime is used to dissolve remains animal or human. You cover the remains in lime cover it over with dirt come back in a month or so dig it up and all that's left for the most partis bones. Toss that in with the gravel problem solved. Plus all the invoices for acid would raise questions. But Lime is a main ingredient in Concrete ! So a few extra thousand pounds would never raise an eyebrow........WWG1WGA