When I first got my pup he howled alot when we went to bed or left alone I left it 3 days and then I got a water spray bottle and just told him a firm no and a couple of sprays with that he soon learnt that howling gets him a spray so stopped. Had to do the same with my bull x when I first got him it took a month to break the behaviour but he got it and just stopped doing it one night. Little things like water spray has a big impact. I prefer that way to going down and "roughing" a dog up as it were.