Yeah, he needs an Elizabethan collar, ie "cone", "funnel" or "satellite dish".
They also make soft, inflatable collars, and wide ones that prevent the neck from bending all the way. The idea is to block the dog from licking the affected area. I'm surprised the vet didn't give you one?
The other suggestions are great too... more exercise, mental stimulation, interaction, play. Wear him out or hire someone to wear him out if you can't.
On the days when he must be kenneled all day, give him a big, raw butcher bone to chew on so he leaves him man-bits alone.
Spray the affected areas with Bitter Apple, or a bitter-tasting antiseptic spray, to discourage licking. Sometimes this works and sometimes it doesn't, but it's worth a try.
Are you considering neuter? Who knows, maybe if you remove what he's chewing on, he'll stop chewing it.
Seriously, though, intact dogs seem to have a bit more of an "edge" to their energy, and everything they do, they generally do just a bit more intensely than a neutered dog would. I wonder if androgens would contribute to the anxious boredom than in turn causes the chewing. Not that I haven't seen neutered dogs chew themselves raw, but I'm just now contemplating whether sex hormones would have an effect on O/C or self-mutilating behaviors.
But exercise, training, play and engagement is key, regardless of his reproductive status.