Whatever monitor book that is, I suggest you chuck it. Or, at very least, stop referring to it for husbandry advice. For a good, up to date book on savannah monitors, buy Daniel Bennett and Ravi Thakoordyal's book, The Savannah Monitor Lizard: The truth about Varanus exanthematicus.
Scroll down this forum, or do a search, and you'll also find information on proper substrates for those species. Savannah monitors do well on dirt that they can dig burrows in, but for best advice check out other people's posts, for I've never kept that species. The black roughneck will probably do well on leaf litter. Look for posts by Dragoon, as she breeds rudicollis and will be able to tell you what they do well on.
Definitely not corn cobs and alfalfa.