There are basically three things you could do here. One: use at least an inch of mulch or stones on the beds to prevent light from getting to the grass shoots. Two: plant the beds full of flowers or plants. The idea there is similar to item one, in that the plants grow taller than the grass and the shade they cast will block enough light to keep the grass from growing even if they do get through. Three: keep cultivating your beds every week!
I prefer item one as it tends to be the closest to "No Maintenance".