Sure those birds are pretty and look sweet perched on your beautiful wooden fence but they also tend to leave bird droppings that are anything but attractive. Bird droppings are also difficult to wash off of your wood fence. Fortunately, there is a very easy solution that won't harm the birds and won't deter from the beauty of your wooden fence.
Drill pilot holes approximately every three foot of your wood fence. Be certain the holes are smaller than your screws. By taking the time to drill pilot holes, you will prevent cracking the wood fence when you screw in the screws. These pilot holes do not need to be deep at all.
Insert your screws into each pilot hole. Do not screw them down flush to the fence. You need a bit of the screw to sit up so you can fasten your fishing line to it.
Fasten your fishing line to the first screw one on end of your wooden fence and proceed to wrap the line once or twice around the top of each exposed screw. Keep the line snug.
Observe the birds behavior. If they try to land on your wood fence the line is in the way and they can't perch on fishing line. They will get frustrated and find a new place to perch. If you use transparent fishing line, nobody will be the wiser - except the birds, that is.