Aura proc stacking

Is there a limit on how many damage procs you can add to an aura and have them all still work? I see the aura for the stone set has quite a few possibilities, since it accepts set IO's for immobilize, slow, and of course... pbaoe.

I wouldn't bother. The chance to proc on toggle powers is every 10 seconds, so it's not worth it.

you can slot up to 6, if your power can find that many procs to slot.

on any power which toggles on, or has a lingering damage over time effect, the IO's have a chance to proc once every 10.5 seconds.

The procs *can* be useful, particularly if your power covers a relatively large area of effect (large number of mobs). For example, on two of my controllers, I have freezing rain 5 slotted with a positron's blast set (including the dmg proc, and skipping the pure dmg IO) for the 6.25% hasten bonus, and 1 slotted with either the slow set or the defdebuff set dmg proc. So that's 2(procs)x20% chance to proc 72 dmg to all mobs in the area of effect, every 10.5 seconds. which amounts to 3 chances to proc before the freezing rain patch goes away. Which is 3(procs over time)x2(io procs)x20%(chance each) 3x2x.20 = 1.20 or a 120% chance of doing 71.75 damage. If we calculate that a la mid's style, that's an average of 86.1 dmg per mob in the area (assuming all mobs survive that long). Nothing to write home about, but it's "free" damage, since I'm casting FR primarily for the defense & resistance debuffs, and secondarily for the knock-up effect, the extra damage is just icing on a character which is otherwise a bit lacking in the dmg department.

My boyfriend has a spines scrapper which does an amazing amount of IO proc damage, I think he has 3 procs in two different aoe toggles, for a total of 6 IO dmg procs trying to hit every mob around him every ten seconds. It can add up.

Usually though, as a rule of thumb, damage procs only perform well on large area of effect powers which can be used frequently. An example of a power which could reap a very high return for the dmg proc slot would be Fire Cages from the fire control set. with high recharge you can spam that every 3 seconds or so, and it has a 30ft radius. Giving you a lot of dmg proc chances. In all likelihood, each fire cages attack will proc on 1-2 mobs for a 72-144 dps bonus per cast. Also, fire cages base damage is only 10 per mob, so slotting it with damage enhancements results in far less total dps than slotting it with dmg procs. Ergo, i slot fire cages for assorted acc,rech,&end and 2 dmg procs, and have a 'spam-able' large area aoe that imobilizes & does about 40dmg on average per mob. It's a quick 1 second cast that I spam in-between almost all my other attacks, keeping mobs 'very' imobilized, doing an extra 40 dmg each (average over time), and holding them firmly on my bonfire (which also has 2 dmg procs in it, which can go off up to 4 times per mob before the bonfire times out).

In single target attacks dmg procs are "nearly" useless.
They are only attractive if you're trying to build up to a set bonus. For example, with Hetacomb (single target melee purple set), the set has "too much" damage in it, and actually performs best by skipping the pure dmg IO, slotting all 4 of the mixed IO's (like dmg/rech, dmg/end, acc/dmg, etc.) and slotting the chance of dmg proc to get the 5slot hasten bonus. Note that the purple dmg proc gives an average of 35.3397dmg per attack (107.09dmgx33%chance), which is more than the 53% dmg bonus which the pure dmg IO gives because it is going deep into diminishing returns.
example: lvl 50 incinerate in fire melee on a scrapper is 347.29dmg 5slotted with the dmg IO and the 4 mixed IO's, and it 'averages' 362.09dmg with the dmg proc IO and the 4 mixed IO's. 6 slotted with all of them you could get it to 382.63dmg, but I generally do not value the 6 slot set bonus on most purple sets. You'd get the same total damage over time by slotting 5 hetacombs (skipping the pure dmg one) and 1slotting a dmg/recharge IO from another set (which wouldn't struggle so deep into diminishing returns), and you'd save a smooth 100million influence, and lose only the 5% resistance to toxic bonus.

In many cone powers, extra range will net you more benefit than a dmg proc. and in any powers which have substantial damage of their own, more recharge will net you more benefit than a proc.

also, they do the same damage regardless of level, so on a 'lowbie' a dmg proc can seem a lot more impressive. At 50, they're sometimes useful to slot, and sometimes useless to slot, but never 'impressive'.

I find that you're better off going for set bonuses than procs on toggle powers. The damage is unreliable and unimpressive.

Reliability doesn't matter. It's like the purple drop rate - in the long run it all evens out.

I guess it depends on whether you're a gambling man/woman. Myself, I kind of like seeing the dice roll every round. I'm thinking I'll put 2 accuracy/end redux enhances on it (whichever ones build toward the best set bonuses), and then 4 damage procs, if all 4 of them are really going to be able to work.

Since we're talking about a Granite Tank here, every 10 seconds is probably better than I'd get slotting it to an actual attack.

Also to note, especially for Stone tanks, damage from an IO proc is NOT modified by the -dmg from granite. From my own usage I found that procs GREATLY enhance a low damage power/AT. I put them in Stone Cages in my earth trollers, and love love love them in mud pots.

i agree that dmg procs are extremely useful in powers that do very little or no dmg, my ill troller has the glimpse of abyss IO in spectral terror which results in it actually being able to participate in DPS every now and then

i like other procs as well which can provide powers with more utility (such as the achilles heel proc in earthquake or sleet/freezing rain)

Not able to access Mid's at the moment...

But will the Perfect Zinger Psi damage proc (taunt set) fit in the taunt aura in Shield Defense?

I'll agree with the other that Procs do more good in low damage powers. That concept led me to create 2 builds that rely almost entirely on procs to do damage.
First I built an earth/rad troller with 19 damage procs in it. Almost every single power, including those that have no inherent damage, are contributing to the spawns defeat. Earth is particularly well suited to this because of all the location AoEs. I just throw everything out there and watch em melt. This toon has become one of my favorite toons, it diddnt cost much and it is very effective.
Motivated by my success with the earth/rad I build an Earth/TA to have even more location AoE. This one has about 29 or 30 procs in it (not all damage procs, some got the -resist or +HP). This thing has so much debuff and damage (especially with the addition of Oil slick and fire ball) its nuts. Dont get me wrong, neither of these will ever compare to a farming build or a pimped out blaster but to be able to easily wipe out +2x8 spawns solo with some of the lowest damage powersets is truly a testament to utility of procs.