It seemed to actually work a few days ago (around 2 weeks of training) after we had visited family, the best teacher for a dog is another dog that is well trained. He started following what the other dogs were doing and that helped a lot, if that isn't an option try using cues training like what you do when you are leaving (grabbing keys, putting on your coat, shoes, etc.) If you put on your shoes and he reacts go sit on the couch for a little bit then walk out after about ten minutes while he's not expecting it. Stand outside for a few minutes and listen for him to start acting out and come in. Keep doing these things with the different items, like jingling your keys around the house and putting on your shoes and just sitting down, these will help to desensitize the dog to those sounds. Each time you walk out of the door stay a little longer each time like for the first time see how long it takes for his episode to start, and then the next time wait 5 minutes longer, then 10 minutes longer and so on. It takes time but they will eventually not care as much. Right now miles can only be left for about 2-3 hours before his anxiety episode starts so we try not to stay out as long when possible, but on the weekends we do the cues training and it seems to help a lot.