Remember to concentrate on finding good people in those markets too.  

I have a triplex that's fully rented out with long term tenants under contract now, and my intention is to now concentrate on sub 30k property's for cash flow.

I am thinking I might throw some concrete mix down the water main access hole to limit that source of water and then concentrate on the exterior.  

The problem is, I am having trouble narrowing down the particular part of DFW I want to concentrate my search.

Your late payments may have hurt your score, so concentrate on making on time payments every single time. 

I find taking some time between houses to concentrate on my home and family is not just good but for me a must!

Big investment firms concentrated on other real-estate sectors—apartment buildings, office towers, shopping centers and warehouses—reasoning that single-family homes were too difficult to acquire en masse and unwieldy to manage and maintain.That all began to change during the financial crisis a decade ago.

If you're security conscious, which it seems you are since you're asking, I'd think in terms of concentricity and redundancy.

I also wonder how the labor market concentrations look in each of the cities. 

Once you know your market well, and know what segment of the market you want to serve, it should be fairly simple to whittle down the list of possibilities to between one and a few that will serve nicely, and concentrate on those.