This may not be the best first option but if all else fails a bark collar might be worth trying. There are tons of different styles out there and many have the option to turn the shock off and will only vibrate or beep if you want. I have a chihuahua mix who barks at every sound he hears and the bark collar helps a lot. The collar I use allows me to turn the shock off (he doesn’t need it) and I only use the beep and vibrate setting but it also has lots of different levels for the shock, the vibrate, and for the sensitivity of the collar. If he is wearing the collar he will still probably bark once but then the beep goes off and he will most of the time stop. Sometimes all I have to do is show him the collar and he will stop. I know a lot of people are against bark collars/E collars but I think they work very well if used properly.