Well, I had a plumber come in to work up a bid for doing all of the under slab work assuming I would do all the digging and backfilling and slab repour myself. He hasn't gotten back to me yet, but he did inform me of the code requirement to have a backwater valve for the basement fixtures. A backflow valve sounds like a good idea to me, but I have read on here about their limitations. Also, I would not really have a way to access it unless I would tear up a lot more concrete and put the valve in the next room over (my furnace room).
I also don't like the idea of digging up my front yard in order to put in a backflow valve outside the foundation wall.