I've recently started using defensive beachheads. They're quite useful, keeping threat further away and providing more warning for incoming attacks.
If I must put a planet on permanant alert, due to an advanced research station or other important capturable on a nearby world, I like to neuter the system and then install a small beachhead (I guess it's more like a desert-head, but you get the idea.) This keeps the ships from piling up in the alerted world. However, what about a situation where the perma-alerted planet links to another high mark planet? For example,
I --- III --- III
Where the Mk 1 planet has your ARS on it. I find MK3 planets take well to being neutered and beachheaded - your defenses don't need to be too heavy to keep it empty, but it still prevents enough of a threat that you kind of worry about it in the back of your mind.
Anyway, it seems that setting up a beachhead sets linked planets on alert as well! As it should be, of course, but a problem. I can't set up a large enough beachhead, or keep enough ships, on the planet to keep it clear without alerting the linked worlds as well, defeating the purpose. Anybody know how many turrets it takes to alert linked worlds?
This brings up another more fundamental question. Does it really matter to have a higher-mark alerted world on your borders? If you never plan on traveling through it, the defenders will only wake up during a CPA, and then only if the AIP is high enough to wake the defenders on that world! With a MK 3 or 4 world, it's possible to keep the AIP under the thresholds, for the most part. The AI will always have enough troops to fill out a CPA, even if they don't exist, so having them on your borders only changes the amount of time it will take them to get there by a few minutes at most. On the other hand, the AI might be goaded into spending reinforcement points on these planets.
If the ships pile up too much, might they start engaging in border aggression, even without a CPA?
So does it make sense to clear out these worlds? Does a beachhead defense seem viable, or should I just use my fleet, which will not place further planets on perma-alert? In the late game, it's difficult to have enough resources to do either, of course.