Beautiful post, as usual, from Diver0001 . . . For me, the single most important thing is to go all the way to the anchor, and note depth and the characteristics of the spot where it has lodged. Getting off the anchor line on the way down has been a pretty good recipe for not finding it on the way back
That said, one of our most challenging sites is an artificial reef on a nearly flat bottom. Every piece of rebar looks like the next, and there is no depth contour to follow at all. Even using a compass is not very helpful, because the structures of interest are spaced sufficiently far apart that it's impossible to follow a straight line. Visibility is typically 10 to 20 feet, too, so you have to get very close to the anchor line to find it.
I have found the answer to that site, though, but it costs about $4000 . . .
That said, one of our most challenging sites is an artificial reef on a nearly flat bottom. Every piece of rebar looks like the next, and there is no depth contour to follow at all. Even using a compass is not very helpful, because the structures of interest are spaced sufficiently far apart that it's impossible to follow a straight line. Visibility is typically 10 to 20 feet, too, so you have to get very close to the anchor line to find it.
I have found the answer to that site, though, but it costs about $4000 . . .