Magma Moat

Whenever fortified land is tapped for mana, it produces {r} instead of its normal type.
Whenever fortified land becomes tapped, it deals
2 damage to each attacking creature your opponents control.
Fortify {3} ({3}: Attach to target land you control. Fortify only as a sorcery. This card enters the battlefield unattached and stays on the battlefield if the land leaves.)