1. Ditches.
Req: Nationalism
Effect: A unit uses ALL of its movement points to enter a Ditched square. Can not be placed in mountains. Will auto-pillage Roads and Railroads if placed on such squares. Can not be destroyed by artillery or pillaged. The only way to remove a Ditch is to have a Worker build a Road on it. Units will be affected by ditches even if they are in friendly territory. Can be seen on the WM if your maps are updated.
Represents anti-tank barriers, barbed wire, tipped-over tree trunks and the like. Would help a lot in MP against the slightly cheesy "Mass MA, blitz, use their conquered railroads and drive them into the sea in one turn" strategy, will buy you valuable turns to form a counter if you have warmongering neighbours and are fearing an attack. Note that it has no effect against units with 1 MP. The downside is the loss of commerce from R&R, and the loss of trade from whoever you're ditching, of course
2. Minefields.
Req: Replaceable parts or Mass Production
I can't believe they didn't include Minefields in the retail. Such an important part of modern warfare, and it's not included in the greatest strategy game of all time? Shame on firaxis
Effect: Hmmm. Not sure on this one, except that it should definitely be included. Problem is: This is clearly a military unit of its own, seeing as it can damage enemies. Military units cost money and shields. Worker actions only cost time.
I think the easiest way to implement Minefields would be to make it a special unit with no attack and 1 MP that you can move around as you wish, and when you press "deploy" or whatever it will kill itself, filling the square with mines.
Though. Should it kill enemies outright, or just wound them? Should it last unlimited, or should there be a cap on the amount of enemies it can stop? Should there be a special unit called the Mine Detector, which can detect minefields, and, in a few turns, neutralize them? You guys decide.
This would be a more effective method of halting an army than Ditches, and is balanced as such with the cost of the "Minefield" unit.
Post yer thoughts ppl!!!