It sounds as if he has separation anxiety. I'm not sure how well those products work, especially for a dog with SA. He would probably end up chewing/scratching at another area (another door or window etc...).
Your best bet would be to crate train him. Speak to a reputable trainer about SA. They can provide with a lot of info that should help you out greatly.

Also NILIS (nothing in life is free) should help boost his confidence, helping him overcome his SA. You make him obey a command for EVERYTHING. ex. If he needs to go outside to potty you make him sit, when you serve him dinner make him lay down, when you pet him make him shake, etc... Don't use the same command everytime either, ex. one time when you pet him tell him to sit the next time make him lay down, etc...

Has he always done this? Has anything changed in his routine or your house? How old is he?

Slowly increase the amount of time you are away from him.

Tell him the same exact thing each time you leave, but do not make a big deal out of it, just a simple, calm "I'll be back" or whatever you use.

Leave him a special toy (filled kongs are great for everything especially SA) and only give him that toy when you leave. This gives him something special & geat to look forward to when you are gone.