Hey Ralph,
I agree the coils should be made better, however most of the water hunting crowd I know have had problems with coils from every brand wearing this way unless they can find or make skid plates (coil covers) of one kind or another or otherwise protect them.
When I am water hunting as I have done about as long as you, I glide (slide) the coil along the surface of the bottom and all its abrasive elements. I've had to repair and or protect every coil I own that has regular use. There are no protective coil covers made for most of them and when they are available they offer their own kinds of problems, such as sand build up and false signals.
Your track record with coils is extraordinary and shows that you are going the extra mile to somehow protect the things or you are very careful how you use them.
My Infinium 8" Mono wore through in about maybe 7 hunts of up to 4 hours each. By wore through, I mean that the outer layer of plastic (on the bottom of the coil) and supposedly epoxy wore through enough that I could see a void inside the coil. I had thought the coil was solid, but found out otherwise. I carefully cleaned and dried what was left of the mono and applied the marine epoxy to fill the gaps and created a thin covering over the bottom of the coil. After it cured a day or so I covered it carefully all over (top and bottom) with the rubberized coating and have been using it ever since the coating cured. At easily a hundred hours now the coating is ready for some touch up otherwise it has been great!
Hard plastics and epoxy are very easily worn by the abrasives they encounter in this kind of hunting and must be protected either by us or at the factory.
Garrett etal. must not view this as a serious problem or they would find a solution. Until they do we must come up with our own solution or start stamp collecting or perhaps needlepoint!
GL&HH,
Cupajo