They are hit and miss. I do not like shock collars at all.
I would say try that, or try Rescue Remedy for pets. HomeoPet also makes some good stress relievers for barking. If all else fails, for severe separation anxiety you can get Prozac for dogs.
I use generic prozac for my cats because they have mental issues. Right now 3/12 are on it. I'd like to just crush it up and put it in their food at this point
but it works pretty dang good. I had tried EVERYTHING else before, and I'm not kidding.. my mom was about to make me get rid of the 3 that are causing problems, that's how bad it was, but we are doing much better now