I prop one or two sheets of thin plywood against our fence and use one or both as a wall for spraying. I use push pins to hold the backing on the plywood. I can always find a sunny day even in winter to spray baste, it doesn't take long. DH bought me two thin sheets of plywood just for this purpose and attached a leather strip on one end of each for handles. They are easy to store in the garage and light enough for me to pull them out.