Two things to note: They scale off much of your equipment so if you're a glass cannon so are they. If you want to build like this go nuts just don't use zombie dogs, they will suck.
What most do:
Stack armor, the dogs become tougher but generally fall off pretty quick still. By the time you get to the goatmen they'll be down in 1 or 2 hits.
What you should do:
Focus on Vitality. I'm running Zombie dogs at level 17 in Act two and the dogs work -still- as excellent tanks. My dogs can tank those glass cannon Wasps you find in the desert and during the Act One fight with the Butcher they didn't die (even with the fire floors)
I'm level 17 have +37 Vit through items and 834 HP and I don't use a sheild. My Zombie Dogs tank, try it out, it'll work. - I also am NOT using the Jungle Fortitue passive. I don't find that I need it.
(I'm not saying this will work after normal or even in later acts but this is in response to people believing that Zombie Dogs suck basically the whole game)