I lost my dog a month ago. He lived to be 21 years old. I am not ready yet but I do plan on getting another rescue dog. As a way to get through my grief, I have been reading books about dog training and dog psychology. I want to be fully prepared for my new little one, given I am much older now and in need of a well socialized companion.

One author that particularly impressed me is Brandon McMillan, a famous dog trainer who had the show Lucky Dog. One of his specialties is training rescue dogs for placement in forever homes. I just discovered where to stream Lucky Dog episodes and found one on dog anxiety that may be helpful for you.
Here is the link: https://youtu.be/D5opI5Pdzco
Brandon believes all dogs can be rehabilitated. Hopefully yours is one of them. It takes patience and consistency. I wish you the best of luck.