defending your empire's borders: what do you do?

[Taera]

Here are some thoughts i can offer:
First and most importantly - as someone (Sun Tzu?) said, best defense is offense. Your systems will be well defended if nothing is coming on them.
Now i know it is difficult to mount a sizeable assault fleet againt bonused AI's and it is extremly difficult to overrun it with earlier attacks but a planet here and planet there is still a loss - of the colony, its production, colony ship and ~0.2 years of construction, plus time for movement. For that my favorite is a destroyer/lc armed solely with PN, rad bomb and a plague bomb. Nasty little thing, leaves a colony completely useless. put ECM, stealth and scattering armor on it, plug in some ressuply storages and/or solar panels and add in a solar sail.

Now for passive defenses, for one - have you tried using the crippling weapons? a single hit from a shield distruptor (say, massive mounted ) can realy leave a ship helpless. Same with a well-shot ID or even tachyon projector.
Then if your the defender you need to work for bigger numbers - torpedoes, WMG, NSP, even GH or some heavy racial weapons. It does not matter how large the reload time if you wont need to reload. Remember, you get the first shot and you start up close - so its a likely hit, and weapons like GH or WMG can be nasty in WP defense.
Something to consider is constructing a BSY on top of the WP and making it build sats, and set it to "launch sats, repeat order". Make it well-shielded and here you go. Or better, build three of these. You get the point.

Overall being stuck on the defense is a dead end - because while your not, the enemy continues to develop and expand, and unless it is finite resources even superior fleets that you put there will be overrun by the sheer numbers that a medium/high bonused AI can produce.

My 2 cents