Striping Off Gold Plate from Silver?

Hello All!

I had a few items gold plated. I guess it is turning because you can
see oxidation (brown spots on the gold). I have two questions- how do
you prevent this? I had some items plated at Red Sky (so expensive).
The undercoat was platinum. Then I had some items plated in town so
much cheaper. The undercoat is nickel. Both plating jobs look like
total crap now. I was hoping I could strip off the gold and go back
to the original silver piece (the items are deox sterling silver).
A) how can I stip off gold B) how do I prevent gold plate from
turning bad and oxidizing.

Thanks in advance!

DeDe