1. LMB: Grenades. I tried using Bola Shot for a while, but out of the generators the Grenades are imo the best choice for a tanky build. The Bolas have a delay that can prove deadly when encountering tougher mobs; also, the Grenades are somewhat faster to clear trash with and seem to trigger LoH a bit more (may just be in my mind though). The biggest benefit, however, is that you don't have to aim at all with the Grenade skill; you just hold down the LMB and spam it, filling the whole screen with explosions. It lets you be more alert with the defensive skills when your main attack is a no-brainer.
I haven't tried the different Grenade runes much, but it seems that Cluster Grenades is the way to go. The reason is clear: the mass AoE makes up for the Grenade skill's inherently poor aiming capacity, turning it into a strength as I just described. As an added bonus, it feels VERY good to have a screen full of spiders explode from the napalm-like fireworks! So far this more than makes up for the relative monotony of the build compared to more 'traditional' kiting builds.
2. Right-click: Here the options are wide open(ish). I'm using Spike Trap with Echoing Blast atm, because I have nothing that can break snares and the LoH from EB ticks while you're frozen, saving your life plenty of times. There is likely to be a better option, but you must keep in mind not to steal too much Hatred from Sentry, which is a major component of the build. Also, imo it's too distracting to try and spam two projectile skills at once (like Grenades + Ball Lightning), although it can be done. This somewhat limits the available options.
3. Shadow Power with Gloom. Needed to put the 'tank' in 'tank DH', 'nuff said. You can spam it constantly if you have an old Nat's set or enough +Disc. I have only the base 30 and it hurts, but the build is viable even with base Disc.
4. Sentry w/ Guardian Turret. The total 50% Damage Reduction from Gloom + GT = sweet cheese sandwich (you may quote me on that equation!). Together with Life Steal / LoH this makes you near-immortal in most situations, depending on armor/res ofc. Aid Station might be another option here, but with 40k life it only adds 400 life per sec, and I'm pretty sure GT is better.
5. Preparation w/ Battle Scars. Tbh I only use this because I have base Disc and need an 'oh-****' button for freezes and stuff. Vault w/ Tumble might be a more logical option, but somehow I hate to use Vault if it's not my actual attack skill. It's very disorienting to dart around like that somehow. This is more of a mental quirk of mine than a sound strategic decision, so try both or even a third skill (maybe Caltrops? Rain of Vengeance?); YMMV.
6. Companion: Boar. The 15% extra res all + 155 life per sec are very good for a tank build. I cannot think of a decent alternative. Yeah, the Boar dies all the time on the higher MP levels, especially since you do close combat. That's what the recast button is for, boyo.
1. Archery. Dee - pee - ess, can you spell it boyo? I knew you could. You can't really use Steady Aim with this build, so use Archery to get some dmg done.
2. Numbing Traps. The 20% extra DR% is the icing on a very cold cake that seals the legend of your immortality. You may learn to tolerate some deaths or have gg enough gear in order to choose something else, but what other good alternatives are there? Maybe Cull the Weak if you've got a nice +cold% SoJ. Hmm, SoJ can also have +12% Grenade dmg. Hail Mary! This plus 14% from cloak means 26% more dmg. Add the extra +dmg% to elites from the SoJ... I think we have a winner here. The only choice then becomes whether to replace Numbing Traps or the third passive with Cull the Weak.
3. I use Perfectionist atm, but I'm not sure I really need it. I think I'd rather give up this than Numbing Traps tbh.
There may be other good passive choices, but I haven't experimented much as of yet. Do report your finds if you have.
Edit: Went ahead and bought a SoJ w/ 10% increased Grenade dmg and 6% cold dmg for 3,5 mill. Sadly it only has 20% dmg vs elites, which may explain the low price ofc. I know the prices of Legs are in freefall due to increased drop rate, but I simply couldn't resist trying this out. So far so good - swapped out Perfectionist for CtW, and both elites and trash are dying that much faster. Definitely give it a try if you can afford a nice SoJ.
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About the potential power of the build: on MP3, I can somewhat tank Xah'Rith's ice rain that would kill me in seconds with any other build. So yeah, nerfbat incoming.
I run MP 3 for keys atm; I only die to Molten, Frozen or Desecrator packs with bad combos, and even then mostly due to carelessness. I think from the pov of keyruns harder MP levels are not worth it with my gear level. On MP 0 and MP 1 the next MP level brings a 100% increase in key finding chance, and the jump from MP 2 to MP 3 is still 50%. After that there's less and less relative benefit.
Here are my stats, for the record:
~400 all res with Boar (I'm transitioning from a pew-pew build; I guess ideally res should be 600-700.)
940 life per sec w/ Boar
2,4% Life Steal
Health Globe bonus 8800 (the SoJ I just bought took away 11k... Ouch! Ideally you should have enough so that a potion heals you to full; this is a very important new stat imo.)
Pickup Radius +6 (You should have 15-20 imo. Hard to get if you're on a budget, as its value is finally being realized.)
1.81 aps (Manticore + DML... Haven't tested 2 hand xbows. Mass LoH may be overkill for survivability. A shield would make you ridiculously hard to kill, but I'm pretty sure it's not worth it due to the lost dps.)
Last but not least,
62k dps w/ Archery bonus included but NOT Cull the Weak (which should be always active due to the +cold SoJ, right?) Low dps as all tank builds, but it is enough for now. Upgrades are very expensive when you don't play very much... Luckily that might change due to the fun I'm having with this build.
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Lastly, pros and cons of the build that I can think of right now:
1. Iron survivability with decent dps. Running to your dying spot is a major timesink in this game; survivability is therefore key for good farming speed (imo). A Ball Lightning build kills trash a bit faster, but the danger from Elites is much bigger with it. Not to mention that it's boring to play (imo).
2. Inexpensive to gear for (relatively speaking). 20-30 million gold will buy you very decent gear for the build, especially if you bid and/or snipe good deals.
3. Customizable to your liking. I'm still experimenting with my right click and the extra spot on my bar, and the passives could likely be adjusted too.
4. Very fun to play with (so far). Although simple spamming may not sound very enticing, I'm thrilled with this build, in contrast to the Whirlwind and Archon cookie-cutter builds which bored me to death (literally enough).
4. Could potentially scale up *very* well with uber gg gear. I imagine tanking the MP 10 ubers may be possible, even easy with 700 res, 50k life and the like. The problem might be that Legacy Nat's gets in the way of other survival stats than Disc in a big way... Someone with a few billion in the bank could do me a favor and try this build out.
1. As it is a 'tanky' build, expect Blizz to pull out the nerf-hammer when the word gets out. Until Fat Jay stops dictating the way that players should have their fun, proceed with caution when investing in new gear for tanky DH builds.
2. Could get boring eventually with the 'spam spam spam' type gameplay of the build. Not a big danger for me, as I loved the Light Sorc in D2.
3. You need *some* capital for the gear to make the build work, but if you haven't got 30 million by now you either play too little or refuse to use the RMAH, in which case you can only blame yourself (imo).