Compared to the improvements that occured in the 10 yrs. from the mid '70s to the mid '80s, we've been in a looong standstill. Nothing but whistles, bells, a little more depth in the last 10-15 years. I've heard that some engineers made something that would show shape in the ground. But their conclusion was that going around looking at fuzzy images all day wasn't effective. It was easier to dig up the thing and look at it 
That was 15 yrs. ago when I heard that rumor from a Whites rep, so maybe now, the Technology is better? Better yet, rather than have something that shows shape, why not something that tells actual composition? Ie: Gold, silver, copper, aluminum, etc... rather than measuring conductivity?
When Teknetics came out with their TID in 1982-83, a rep. came to our club meeting, and did a demo. Everyone's jaws dropped when he waved a pulltab, and it gave a certain sound, then he waved a gold ring, and it gave a different sound! A nickel produced yet another sound! Several guys thought they were gonna get rich digging nickels and gold rings and bought them. Then reality set in, that there's still a heck of a lot of aluminum shrapnel that mimics nickels and gold rings 