Good idea for no digging in my rock solid ground. Do not cover the holes but use them for herbs and annuals. line with weed barrier cloth and used rebar in several places for stability. I love it and makes maintenence super easy.
Concrete yard ornaments can easily and inexpensively be made and add new dimensions to your backyard retreat. Here is a simple bird bath that looks good in any yard. Try different shapes. Add stones to the middle for interest., With the concrete.