What about a mine UNIT...
It either
1. Has a range of five and once you click a tile to place it on it doesn't move until you destroy it yourself or the enemy rolls over it.
2. Movement of 1, defends only.
It would have an insane bonus on armored units, for example, but a moderate to low strength so infantry (e.g. real life minesweepers) could disarm them. However this brings up the problem of enemy aircraft killing them off, and the unrealistic gunships vs. landmines scenario... lol.
Perhaps they'll be able to do something with it in CIV V