I'm not doing anything particularly fancy with the Lightnings on most planets, it's more a reminder not to leave them out of your turret setup. Kahuna's trick of course works well, but you can't really do it on every planet since you'll run out of FFs and Tractors. (At least that's true if you're not dropping a huge chunk of your K into turrets and FFs, so far I have been putting the lion's share into my fleet and economy to feed the starships and rapid-deployment warheads.) But I still like to include Lightning turrets on my not-full-choke planets -- depending on what the AI has, I'll drop them either at the leading edge of the FF covering the command center, or towards the front line of the main turret array, near the MLRS line.
Ideally, I like to have Grav coverage almost up to the command station FF -- so anything that is sniper or missile immune, or that just survives the barrage of the longer-range turrets, gets pounded by the Lightnings as it slowly crawls up to the turret wall. Single-digit movement speed is almost as good as getting grabbed by a Tractor, especially as Grav III has a long range, can affect infinite stuff, and it seems like less stuff is immune to it than tractors. The Lightnings don't last as long without the FF coverage, true, but I have yet to commonly run into situations where I really care.
Most of the time, by the time the wave gets within Lightning range, it's so banged-up by all the other stuff shooting it that the electrical burst finishes it off before it can shoot back. It results in a lifespan that's "Good Enough" generally -- I'm not nearly as possessive about my turrets as I am my fleet. And I always keep some Engis and Rebuilders on every planet so stuff gets repaired under fire anyway, and I check up on them after waves to make sure the little repair minions keep their population up. This is one reason I always unlock at least Mk.II Engis, and if I can swing it, Mk.IIIs are lovely. I didn't have them my last game and missed them.
And if whatever it is that's stepped onto my lawn is bad enough that I'm genuinely concerned about it actually burning down my turret arrays and my fleet is busy elsewhere, that's what the Missile Silo or warhead Warp Gate is for. (Think of it as an ICBM turret.) Unless it's some utterly pointless backwater I have no intention of trying to hold, or something walled off out of reach of the enemy, I will have one of those on every planet -- I guard my empire with a (sometimes nuclear) warhead umbrella. Important places get a Silo so in a crisis I can avoid the 20-30 second warp paralysis (lesser priority planets, or ones that don't normally take waves get warp gates as they can generally afford the small delay). I also tend to keep a LOT of Engis on those planets.
About 12-15 Engis dropped on a silo can crank out a Lightning Mk.I in 18 seconds exactly (seems to be the minimum the build time can be reduced to) -- if the impending attack can flatten your planet faster than 18 seconds, you've probably got a problem bigger than what turrets can solve. The only question at that point is -- do you want to ignore it, recapture it, or has the enemy concentrated so much of their strength there that it's worth considering speed-building a Nuke and sacrificing the planet permanently to deprive them of such a large chunk of their mobile forces? 20-30 Engis can pop out a Mk.I Nuke in ~35 seconds if you have the economy for it, so it is entirely possible to deploy nuclear weapons on the fly...
Then again, some might say I have a somewhat... unorthodox approach to defense at times... Will it work at extreme difficulties? Probably not due to the AIP hit. Then again, maybe it could, if you could play a fast enough game to not have to go through the cycle too many times. Personally, I look forward to the careful and thorough testing that these theories require. >D
