On Monday I introduced some simplified Basic Set armor compatible neck protection for a DF game. Basically, to offer more options that the current Greathelm, Mail Coif, both, or nothing choice.
There are other ways to go.
Use the 3e Rule. Basically, that rule is using Torso armor unless you have a heavy helmet.
The tricky bit here is that this implies that torso armor covers the neck - front, sides, and back. Okay so far, but then you put on a heavy helmet - they should stack if that is the case. If it stacks, this means either you waive the penalty to DX for stacked neck armor (hey, it's part of the head, in contradiction to p. B282), or you apply it. I can't see waiving it. Yes, that's simple, but your ability to freely move your head is restricted by lots of layers around the neck (especially interlocking layers). Applying the penalty means giving a -1 DX to anyone with a mail coif (or modifying it so it doesn't cover the neck anymore) and Greathelm (shades of 3e again, here.) Since the penalty is per-layer not per-location, this means those guys may as well go ahead and add another layer everywhere.
It also means DR on the Neck suddenly goes up for heavily armored fighters, changing it from a potential weak point into a strong point second only to the skull.
This one only sounds simple, in my opinion.
Use Torso DR. Per B282, Neck is part of body. With this rule it is assumed to be included in any Torso armor protection. This just makes it, much like Vitals, a high-damage location for certain types of attack, but otherwise no more or less armored than the torso. It's -5 for an additional +0.5x damage for crushing or cutting.
This is by far the easiest, but it makes Neck much less valuable of a location.
Use head DR. As above, but treat it as covered by head protection.
Tricky because, which head location? Skull? That means a skullcap pot-helm or cloth cap also gives neck DR. Face? Mail coif loses Neck, Greathlem loses its prime benefit of all-over protection, and Leather Helmets gain Neck. Kind of an odd problem. You could say, however, it is Skull from behind, Face from the front, and anything that says Neck already covers it from all angles.
Out of those three, "treat it as body" is probably the best. I still prefer the additional armors from my previous post, however. The neck still has value even if torso DR covers it, especially for high-damaging cutting weapons. Or against The Kurgan.
It's worth noting, of course, that DF is full of monsters that have Injury Tolerance (No Neck) or (Homogenous), ones with universal DR that isn't differentiated by location (in fact, that's the default), and threats where neck chops won't do the job even if they do damage (anything with a hit location specific Unkillable weakness.) This mostly affects PCs fighting high-skill opponents.