Somewhere back in this thread it was asked, "why dig 50's it's junk?'. I dig 50's because gold comes up in the same range as nickels and pull tabs.
I dig a lot of pull tabs, but that's so I don't miss gold.
As far as ground balancing goes. I ground balance at every new site I visit.
I pick a clean spot and ground balance it there, if there is a target underneath my coil I will dig it up and start again.
True story.......I went to a local park last year and did my usual ground balance. As I said there was crap under the coil (it was a trashy area) so I figured it was easier to clean the trash than it was to find a clear spot.
I dug two items in the same hole, 1 bottle cap and 1 x 14k gold ring.
As far as salt water goes. Garrett has a hard time doing a proper ground balance with salt water and the AT Pro, so you will have to mix and match your machine to the area you are in.
Good luck.