I can tell you that after having them in the ground with coastal out here, I am pulling them and putting them in a very large container. I have a few tubs from molasses licks for the animals that I will put them in. good luck. I am eager to see what others come up with

The only thing I can think of, and this is assuming that the Google search that I just did that said "coastal Bermuda grass" as the first choice was correct, is to clear a pathway around the plantings and diligently keep that pathway clear of the Bermuda. Maybe dig down and put a barrier along the outside edge of the pathway to keep it from spreading underground, which I've suspected Bermuda of doing before. I'm not even sure that a container will work, as I wouldn't put it past the Bermuda to come in via the drainholes and grow up through the entire container. It's very tenacious.

The suggestion of clearing a pathway and using a barrier is a total waste of time. I raise coastal and a couple of other varieties of hybrid bermuda. The root systems of these grasses will extend down beyond 6 feet. To encourage growth and thicken up a stand I plow and disk as if i was trying to kill it. The only way I know of to control it is with the repeated use of that terrible word we hate to hear, herbicides. Not only in the path but for a good way beyond the path. The roots will simply grow beneath the surface an into the berries if you don't.
When I mentioned repeated use I was serious. I spray hay fields in the spring with roundup, after the emergence of the coastal. The grass is knocked back a bit but comes back quickly. I have been trying to kill it out of a 2 acre garden for 5 years now.
Good luck.

ditto novascapes. My grandfather also raises coastal and his blackberry patch is completely mixed with coastal. The good news is it doesn't seem to hurt the berry production. It's just messy having it all growing together.