There should be defenses that are useful only when the players are outside the base. For example, a structure could hurt team mates more than the enemies and hence activate only when there are no team mates is nearby.
Nuclear turrets have infinite range and shoot beams of cancerous radiation that damage and poison aliens, but they also damage and poison any humans within their line of sight, while also permanently reducing their maximum HP (down to the minimum of 10). So, unless an override command is issued, they hold their fire when there are humans nearby.
Mindful eye should be the alien counterpart of that. Should create hallucination and slow all humans and aliens in its sight, slightly damage humans and prevent aliens from using their special moves, i.e. pounce, trample, strafejump (so that aliens can't longer catch up with them).