These homebrew rules gives Marines another option when trying to stay alive against the Alien hoards, at the cost of offense and mobility.
During their turn, a Marine may spend 1 Action to “Defend”. This means that they are taking cover, dodging, or otherwise attempting to evade attack.
A Defending Marine gains a +1 Defense Bonus to any Alien Attack, Acid Spray, or Grenade Hit (if using the Alternate Grenade Rules) roll against them during the “Marines Move/Fire” Phase of the current Turn, and during the “Aliens Attack” Phase of the following Turn.
For each Action spent Defending, a Marine’s Defense Bonus increases by +1.
Example: Hicks uses all three of his Actions to Defend; because he’s using all his Actions, he can’t move or shoot this turn, but any Alien Attack, Acid Spray or Grenade Hit roll against him during this Turn’s “Marines Move/Fire” Phase or the next Turn’s Aliens Attack” Phase will have a +3 modifier (in addition to his Melee bonus, when applicable).
Obviously, this optional rule can greatly improve a Marine’s chance of surviving Alien attacks, especially if that Marine also has a high Melee value, however note that Actions spent Defending cannot be used to move or shoot, meaning that eventually either they will be surrounded by and overwhelmed by multiple Aliens, or simply run out of turns to achieve the Scenario objective.