I've not got a wording yet just an idea based on something that happened in International Incidents. Basically VIZion launched a chemical weapon at the British Londunium capital.
My proposal would do the following.
Ban attacks with NBCs, carpet bombing, F.A.E.B's, "Bunker Busters" or artillery and rocket bombardment on residential areas still containing civilians.
Ban military forces being kept in residential areas.
Breaking the above terms constitutes a war crime.
If other strategic targets such as factories, shipyards or airstrips are in residential zones only guided bombs weighing a ton or less, or cruise missles of that size or narrow beam energy or laser weapons may be used to prevent civilian casualties.
Thoughts? Additions?