Make a backyard bowling alley. Add food coloring to clear plastic bottles of water. Use party streamers as lane margins. Add glow sticks for night bowling. (These would make great outdoor table nightlights also with the glowsticks, gonna try it!
DIY - Glow in the dark pots with mums for fall/Halloween. Buy a flower pot that you really like and use Rustoleum's Glow-in-the-dark paint to paint the pot. During the day, the paint will absorb the sunlight and at night the pots will glow.
I don't have a fence, but like this idea. Find old windows, replace the glass with mirrors and put these on your fence (if you can). The mirrored image of your garden on the fence will make your yard look bigger. It's an easy trick!
What a cool idea this is! Outdoor Chandelier: Replace the light bulbs in an old chandelier with inexpensive solar lights & hang it from a tree branch. You'll have gorgeous outdoor lighting without having to hook up electricity.