Painting Fence Panels

Go to a proper hardware or paint shop with a picture and ask for paint recommendations. I think you need to clean and prime the concrete and then paint it, it's too smooth for the paint to stick otherwise.

I like Ronseal Ducksback for wooden fences. I wash them down and go over them with a stiff brush to remove any loose particles before repainting.

You might need to remove the paint before using the primer so it sticks, but the staff in a proper shop, not Woodies etc, will know.