This is what I've done...because we have weeds so bad here. I had every last bit of vegetation ripped up , it was mostly weeds anyhow. The soil was tilled, and I had St. Augustine grass layed. We have had it for 2 years, and not one weed has sprouted up on our grass. I have the grassy area confined to a large patch about 50x50 ft. Around the grassy area I used edging to keep the grass from growing into the flower beds. In the designated flower bed area, I layed a ground covering to smother the weeds, and over that I layed river rock. I also designated areas for vegetation, and planted big bushy, but pretty plants to fill in those area. Doing that has kept the weeds out. I occasionally have a small weed here and there to pluck out of the vegetated areas. I am currently working on the rest of the bare grassless area. It has taken so long because it is so expensive for the river rock ($5 a sq ft)......but I'm doing a rock garden of sorts, with stepping stones. I will be posting pictures once it's all done.
I will admit we have used chemical weed killer a few times, because the weeds have gotten so out of hand. I feel aweful, but it gets SO overwhelming at times. We have a flower bed in the front of our house that is 24 ft. wide, and 10 ft. deep...and it's a 2 tier bed. That thing has gotten so filled with weeds, we just had to do something. We have pulled all of the weeds from that bed before, and it took the two of us a total of 15 hours...hunched over. This last time I just broke down and had my husband spray it with weed killer. We are going to be planting in it real soon, and covering the exposed ground with a cover to keep the weeds away.