Thanks, I knew there was something I meant to post about - undermining!
If an army of at least 6 units makes no attacks on a turn it may attempt to undermine the enemy (place a mining marker for each mine costing 1 IPC).
If, at the beginning of its next turn, it still holds or contests the tt, it may attempt to explode the mines by rolling a d6 for each:
For every roll of 1 the mine explodes prematurely and kills one of your own units.
For a roll of 5 a mine destroys 1 enemy unit.
For a roll of 6 a mine destroys 1 enemy unit.
You must go ahead with any planned attack irrespective of mining results.
Needs to be some rule covering enemy counter-mining.