Placing bricks in a growing area is using them for a mulch - a stone mulch could also be used. Probably any stone half the size of a brick couldn't be moved by a hen.
Our flowers are mostly in the front yard and the hens learn not to go around the house to the front yard. A
monster shows up out there and threatens to eat them raw! Or, so the hens must think
as they race back to the safely of the backyard. (They stay in their henyard unless someone is outdoors and that happens a lot during the Summer.)
An herb garden is in the backyard and it also is out of sight from their coop so they don't spend much time there. If they want to have a dust bath, the soil under the deck is handy. They have never done any damage to the herbs other than scratching around them. I'm not saying that no chicken eats herbs but my hens have never done so. They have a choice of lots of different mints, chives, basil, rosemary, sweet marjoram, oregano, thyme, anise hyssop, sweet fennel, and probably a few more that I can't think of. But, they obviously prefer the grass and clover in the lawn.
The fact that they don't bother so many of these "mint family" plants makes me think that you
may be okay with raising the ornamental mints. Those would include - salvia, monarda, lavender, perila, ajuga, catmint, coleus, and some others . . .
Maybe other folks have experience with these plants and their chickens.
Steve