I was thinking that cinder blocks would be the best and planting marigolds in the divots would be good because many animals dont like the smell of them.
Let your imagination be your guide.
I have a couple of cinder blocks at the end of one of my tiny planting areas and I plant marigolds in there every year. They usually do very well but in those cinder blocks the soil dries up and you can’t miss any watering days.
They get pretty big sometimes too.