I've heard great stuff about a food called Avo Derm, so I might give it a try next time.
I honestly have never had trouble with any of them affecting the health of the dog. The digestive tract of the dog is the digestive tract of a scavenger. I think they're probably just fine getting just about anything, expecially if it's varied. My own uneducated hunch is that perhaps, if anything, the restriction of the diet to just one uniform food for their life is probably not what they're best suited to have, any more than we are. And food sensitivities that develop may in fact develop because they are given only the same processed food for too long.
So, though I feed premium foods (I loved Iams Eukanuba and only stopped feeding it because our easy feed store stopped carrying it), that's mostly to avoid what I think is horsemeat, or just plain corn filler crap that just leads to too much crap in the yard ;~D. I think most of these decisions are based on our preferences and politics and desires... Dogs would be just as healthy scrounging the garbage and drinking out of mud puddles.