Shadow boxes are great decorations as of a wooden fence as of a brick wall. They also provide some additional storage space and are great to display some of your indoor plants during the summer season.
These shadow boxes are made of crates bought at a craft store for less than $10 each. They are usually unfinished so you can stain or paint them however you like. You can hang them any way you like: vertically, horizontally, in large groups or just several of them.