Bit of advice neighbours dog barking

My neighbour has a dog and he has recently started barking/howling/whining whenever the owner is out and if its getting on my nerves its surely annoying the whole neighbourhood. He did this as a young pup but got over it and has been well behaved and quiet up till the last few weeks this just started out of the blue for no good reason we've been able to fathom, my neighbour is now a single man and of course has to work/have a social life but the dog just makes so much noise when he's alone. He has a plenty of space in the garden with large kennel/toys/food/water and I do feel a bit sorry for the neighbour as he is very fond of his dog and always runs him before and after work each day and is really upset that the dog is causing the neighbours to complain about the noise. He can't be left in the house as he is destructive.

So any suggestions what he can do? I thought about suggestion one of those electric things that are supposed to curb a barking dog but I don't even know if they work or how. I've tried going in and spending a few minutes with him during the day but it doesn't help as soon as I leave he starts again . He is too boisterous for me to walk him and needs a strong arm to walk him. I'd be grateful for any suggestions as one neighbour is threatening to call the RSPCA , whether they would do anything or not I don't know.