Bruce Fogle D.V.M has written a excellent/usefull
paperback book called
"The Dog's mind" put out by Howell Book House.
There is a section in his book that
deals with the causes and several
treatments for separation anxiety.
Deparking or a barking collar is
not mentioned.
If you have not given up yet, and you
still have the time and patience to give
it another try.
Might be worth the $15.00 to read the book and see if there our any ideas you have not
tried. (I also would not rule out
the help of a private trainer.)