Landscaping - keep bermuda out of flower beds

Ive got bermuda grass and it will simply not stay out of my flower beds. Ive tried trenching, but the shoots that have already come up, keep coming up after I pull them. A year ago, I dug out the beds, laid down weed barrier, then a thick 3-4 inch layer of cypress mulch. Still, the bermuda finds its way into the beds. So today, I said enough was enough and hit the areas with roundup. Its gotten so bad that If I dont tend the beds for 2-3 weeks, the front parts of the beds will start to resemble the rest of the lawn!

I have plans to completely overhaul the beds with more landscaping, but I want something that is very low maintenance. Im considering some ornamental grasses and plants. My main concern however, is keeping the bermuda in check, WITHOUT having to pull it every dang week!

I have a similar problem with zoysia grass. I use roundup periodically around the edges of the beds. I find that this takes less time than pulling the grass. I supposed that some sort of edging set deeply enough into the soil will keep the grass out.

Hope this helps.