I think everyone as mentioned what I would advice. Its all in the rows and I mean hit those rows from every angle BB bent overs, T-bar,hypers, single db, deads and many of the machine rows what are in our gyms.
I stopped doing deads along time ago if I do them now its very light with constant tension like AG mentioned, I don't even mention them in my workouts because they just a finisher in some of my workouts but when I stopped doing deads due to injury I was told to build rods of steel down both sides of my spine. So I spent months/years attacking my back, I concentrated on my back thickness in particular and started doing a lot more hypers like I was told to and my back especially my lower back exploded. I couldn't believe it to be honest because I was powerlifting for yrs and never had a lower back like I built after I was only doing rows and hypers.
My back feels strong but problems occur when my spine is being crushed with weight so that's why I only go light with deads but I am a big rower and a heavy one. On hypers I will do weighted ones which I slowly built up and then I started to twist at the top of the hypers and lock in both steel rods going down my lower back, I could feel something very strange and powerful and within months I produce some serious rods supporting my whole back but my lower especially. This photo isn't a back pose and I was hunching over with my shoulder so myt tattoo artist could get the picture of the work he just did, so my lats aren't flexed and shoulders are rounded but you can see how my lower back is supported by rods of steel, its like a canyon down there. Oh and the width also exploded with rows in conjunction with my walnut cracking but rows I think I am built for them, my back responds well to them but trust me when I train my back I knock hell out of it, a lot of guys don't train it hard because they don't see it which is a mistake, thickness from your back creates some funky illusion
On rows and this can be with a BB,T-Bar or db's I really lock in my lower back and keep my elbows close to my torso and use my back to pull or drag the eight up my thighs, its hard to get right but once you do you can start pilling on the weight and still have that focus. I see many guys rocking the weight but my lower back is locked in and doesn't move until failure comes in.
I have various other methods attacking my back with rows with db's but its all mind muscle connection once that's right you can take the bicep out of working and just let the hands be hooks and pull with your back