What kind of paint did you use? How did you attach these to the fence? Did you drill holes? Did you use gravel or rocks for drainage?
I was searching for the same information as you. How it was done, i am thinking i will have to guess and as you question drainage i guess and guess only it is by drilling holes in the cans at the bottom.The same as my pots on the ground.if it works there it makes sence that the same applies to when putting the pots on the wall