The concept for this is VERY simple and it works GREAT.

It's a one-arm dumbbell row, however, instead of setting your non-working hand on a bench, you will instead be setting your hand flat on a wall in front of you, then supporting your body using an isometric plank hold.

While you're holding this position, you're going to do the dumbbell row. This is going to target your back very strongly (especially the lower/inner lats, I've found) AND your core at the same time.

First, set a dumbbell you could normally use for about 15 to 20 reps a few feet in front of the wall. Set your palm flat on the wall at about upper abdominal/lower chest height (when standing).

Keeping your hand on the wall, reach down and grab the dumbbell. Lock your core down TIGHT when you pick up the dumbbell, and make sure to keep an arch in the lower back as you're doing the exercise to protect your lower back.

Now step your feet back and set them about a foot or two apart, so you're forming a triangular base of support with your hand and feet. The dumbbell should be hanging straight down at arms-length.

Now row up, just as you normally would for a one-arm dumbbell row. Hold the contraction at the top, for a second or two, and really try and pull your working-side shoulder blade "across" your back as much as you can.

This is what's going to really help with targeting the lower/inner lats...this is especially due to the opposing tension of the static hold on the other lat.

Just holding that plank position with your hand on the wall, even without the rowing, is going to work your core. Throw in the row as well, and you dramatically increase the core stabilization required for the exercise as your core must dynamically stabilize your body as the weight changes
position.

This hold actually works the lat and tricep of the holding arm, too.

The higher you set your hand on the wall, the easier the hold will be...the lower you set your hand, the tougher it'll be. And if you go low enough, you'll have to push HARD with your legs as well, to keep your body wedged and stable in position.

One you finish your reps on one side (and this can really be ANY rep range you like...anything from very low reps to very high reps, depending on your goal and the weight you're using..and your core strength!), I recommend taking a short rest (at least 15 to 20 seconds) to give the lat on the static  hold side a bit of a break, then work the other side.

You can also hold the dumbbell in an underhand "curl" grip to change things up. This can actually help target that lower lat area even better.

Using an overhand grip and coming up wider to hit the upper back is possible with lighter weight...and it does have to be lighter because at the top, the dumbbell will end up well outside of your base of support..and a heavier dumbbell will tip you over.

The only downside to this exercise is that you may be a bit leery of suporting yourself with your palm flat on the wall like this. Personally, I think this actually FORCES greater tension into the muscles of the back and core.

However, if you prefer a more "stable" version, try this version using a bar for your hand. 

I just have a bar set on the rails in the power rack. You can use a Smith machine, or really anything solid that's about 4 feet off the ground.

This allows you to grip onto something rather than relying on core tension and friction to press your hand into the wall and not slip.

The rest of the exercise is done exactly the same.

As in the previous version, the higher the bar, the easier the "hold" portion of the exercise will be.

Next time you hit your back, give this version of the One-Arm Dumbbell Row a try. I'm a BIG fan of exercises that target the core strongly without compromising workload on the target muscle. This is a GREAT example of that philosophy.