If a counter is for a unit that is not deployed on the board, because it is in reserve or for any other reason, then there is a chance the counter represents a booby trap or minefield instead. Roll a D6: on a 4+ it is a booby trap or minefield (defender's choice), otherwise it is just a dummy – remove it from the table.
Booby Traps: The player controlling the booby trap may choose to detonate it when an enemy model or unit is within 6" of the marker. As usual, the owner of the target unit chooses which model takes the damage and resolves a single Strength 8 hit, Armour Piercing 2, on him. Unlike minefields booby traps only work once, so remove the marker once the attack has been made.
Minefields: A minefield is an 8" by 4" rectangle, placed in contact with the hidden counter.
Any enemy model moving over a minefield triggers a mine on a roll of 4+, taking a Strength 6 hit with no Armour Piercing value. Vehicles take a Strength 6 hit against their rear armour, but all penetrations are glancing hits only.
Skimmers and Minefields: Minefields will contain specialised devices with proximity detectors, the ability to leap upwards, or simply detonate in such a spectacular fashion that being a few metres in the air is no defence. Because of this, skimmers and troops with jump packs are affected by minefields just like ordinary troops and vehicles.