I'm a big fan of Karl Von Mueller aka Deek Gladson, aka Charles Dean Miller. IMO he is the patron saint of modern metal detecting --- full stop. I currently own #6, #7 (which are distinctively different), 'Sudden Wealth' --- my favorite and 'The Master Hunter Manual'. The latter is basically just a puff piece written to promote Garrett's top of the line BFO metal detector from the early 1970's. In there though is some great advice on metal detecting including the earliest description I know of on the "Halo Effect." I've also read his 'Encyclopedia of Buried Treasure' and the 'Treasure of the Valley of Secrets' which was the only disappointment in the whole bunch.
A rumor goes that KVM and Garrett had some type of falling out. After that Garrett asked KVM to remove the last part of the original #6 describing how to make your own metal detector. Then some treasure hunters felt like KVM was giving away too many of their secrets and his publishing office was burnt to the ground including most of his research. This set back was said to have hastened his death back in January of 1990. His last address I believe was in a small town called Segundo, CO. The real expert on this guy and his works here on T-Net is Old Bookaroo who I think reprinted 'The Encyclopedia of Buried Treasure shortly thereafter.
There's a reason why KVM's books are in short supply and in high demand on Ebay.
HH
-spyguy