I love/hate bermuda grass. The best way I know to keep it in it's place is to imbed a wall barrier around the exclusion islands. The barrier needs to extend at least eight inches below the surface and at least four inches above the surface. The barrier needs to be a material that can tolerate a weed eater, else you will have to pull invasive runners by hand. Finding such a barrier material has proved difficult for me.
When the barrier is installed, make sure every speck of bermuda grass stems and roots are removed from the island.
As for glyphosate as a control means, my experience has not given much satisfaction with bermuda grass. The grass is very resistant to it, and the concentration of the mix and/or the frequency of sprays have to be strong to kill it. In addition to that, preventing overspray is difficult. Another problem is that runners that get sprayed take the spray back away from the point where the spray is applied so that a nice clean border is not established.