My POS, currently near death's door, is a large dickstar. (This charming name for it I found online, not my fault.) The design uses almost all ECMs, along with a modest number of guns and webs, etc. to make it possible for the tower to focus enough nasty to kill a solo pilot who accidentally uncloaks. But it is the ECMs (and shield hardness, to some extent) that are the crux of the idea. My tower has some 40 ECMs, around 10 of each kind. However we also have an x-large ship maintenance array. (In retrospect, bad idea; see below.) By skimping on ship storage we could get up around 64 ECMs.
Now, I don't know exactly how ECMs work in the event of attack. (I should have paid more attention in the recent unpleasantness.) But my naive model for what they do is randomly pick a ship, then lock it and jam it. Then they randomly pick again. So they will waste a fair amount of time locking and relocking. Still, each jam hits with a jam strength of 15 if it's of the wrong flavor, or 45 if it is lucky. 45 will jam about any ship other than those with ECCM, and even them, often. Even 15 will jam most ships most of the time. (Most battleships have a strength of around 25, and the chance to jam is the jam strength divided by sensor strength, so about 60% against a battleship.)
So, to attack a dickstar takes a substantial number of ships, especially at the beginning. A fleet of 20 would spend most of its time jammed out. The chance for any given ship to be jam-free for a cycle is about (19/20)^50, which is about 7.6%. Of the ones with at least one jammer attempting, at minimum 60% are jammed; many have more than one jammer trying or they have one of the faction-specific auto-jams. It's harder to analyze this mathematically, so I'll just wave hands and declare another 5 ships are jam-attempted but once; about two of them will thus go unjammed. So some damage does get through, usually about 3 ships. Against 64 ECMs, it's worse. Anyway, it was until Rubicon.
Enter bastion mode. The bastion module was introduced in Rubicon, and only Marauders can fit them. In bastion mode, a Marauder gets much more tank: 30% more hardness for shields and armor, which does not have a stacking penalty. Also, it gets +100% shield and armor self-repping. It becomes ECM-proof. On the downside, it is immobile and cannot get remote-repaired. But the ECM-immunity is the key. A fleet of 10 Marauders (this is what the Late Night Crew brought to my system) can simply ignore ECM. They can focus on any defenses which they don't like, with full fleet firepower.
A marauder in bastion mode can rather easily tank anything on a tower, excepting neuts. For example: a Minmatar tower can dish at maximum about 2500 omni DPS with decent range -- and that if it only onlines guns. Get out your EFT and design a Golem with a Pith-C extra large shield booster, and otherwise tech II. Get the cap-stable tank above 2500. Pretty easy. The only way a tower can possibly kill a Golem like this is by neuting it out. If you are willing to control shield repairing by hand, you can get an even better tank. You can also push the tank to impressive levels by spending on faction stuff.
So what about a POS with lots of neuts? Well, for one thing, neuts are very hard on your power budget. Every neut you online means taking offline about 200 DPS. But also computer-controlled neuts are just as stupid as ECMs. They won't try to neut out an enemy, and then keep him flat while hammering with guns. They'll neut a bit, then randomly pick a different target. Neuting a bit here, a bit there, won't slow down a fleet larger than a small gang at all.
Still, even if it is rare, a few neuts which luckily focus on the same ship for a while, along with guns applying damage, would get some kills. Marauders are quite expensive. So it's worth thinking about how the Marauder fleet might counter the threat from automated neuts. And that's pretty easy, actually. Have a mobile depot; deploy it where you are parked. Now if the tower starts really neuting hard, swap out low-slot items for capacitor flux coils. Voilà! A dramatic boost to cap recharge. Once the neut moves on and the capacitor rebounds a little, swap the damage mods back in.
This does require a bit of attention to the capacitor. However, it only requires attention during the relatively short period when the attacking fleet reduces the neuts, which is probably the first thing they will do. Once the neuts are all incapacitated, the fleet is safe from anything the tower can do.
What about neuts and guns with humans running the weapons? Well, that would work. But I cannot rely on it, and probably you cannot either, unless you are a relatively large corp. There are large swaths of time when I am sleeping or at work. Since I want to play at the same time as my few corpmates, I discriminate against people not my general timezone. Thus my tower has large periods of non-coverage. All an attacker would have to do is consult a killboard, searching for our kills. Or, for that matter, don't even bother with research. Just attack. If an enemy actually appears in time to man guns, and he has neuts to use and is using them properly, pull out. Or use logis with ECCMs.
So what about defending with a larger fleet? That works. Bigger blobs beat small blobs, other things equal. But I don't have that fleet, and you probably don't either if you're a relatively small corp. And of course a fleet, like POS gun operators, won't be around most of the time anyway except for a very large corp.
Right now I feel the only defense for the small POS operator is cheapness. So, don't use X-large ship arrays. No capitals, or at most one carrier. Ships overflowing? Cut the fat. I violated both of those rules, and that's probably a significant reason why the Late Night Crew chose to attack my POS. More loot is better than less loot. Make your POS shield hard (44%). This at least buys some time before your POS is reinforced. With extra time you might get online and can move stuff out of storage into ships.
There's one other thing that would work: occupy a C1 wspace system. Marauders, like battleships, are too massive to enter C1. You can still use dickstars in C1. Gevlon has a good primer on occupying C1 that he recently published at his blog.