dolesorchard,
I see that you prefer salt water to fresh water. I see that you are from Maine. I see that you are flying into DFW airport. We need to recalibrate your distance measurements to Texas size. Lake Travis (Austin) is considered to be close (nearby) to D/FW. It is 3.5 hours away.
One saltwater dive might be something out of the Galveston TX area. That is approx. a 6 hour drive one-way from D/FW. Your next best saltwater option from D/FW is in Destin, FL. Yes. I said Florida. Your third closest salt water option would be South Padre Island / the Texas Clipper. South Padre is about an 11 hour drive from D/FW and yes it is still in Texas.
OK. Freshwater options. Most folks around DFW make very frequent (and short) drives to Clear Springs Scuba Park just outside Terrell TX. It's about 1 to 1-1/2 hours from Dallas. Other options exist. Lake Travis is real popular around here.
Then there is Lake Murray, Oklahoma. Athens Scuba Park in Athens, TX. The next freshwater dive option is about 5 hours away.
jalistair,
Check the dive conditions report "stickied" to the top of our forum. A bunch of us dive CSSP on a very regular basis.