Spraying a Picket Fence

Hello,

I have a wood fence that is surrounded by neighbors that needs to be sprayed with a stain. I plan to hang a cloth behind the fence to catch anything that goes through.

However, I am not sure how to handle the pickets at the top of the fence. Since, I don't know how to mount a cloth even with the pickets to catch the paint that will go through the spaces. Can anyone tell me how they do this?

This is a large fence and brushing it would take too long.

Thanks,

Randal