2nd time I've had someone come to me with this problem. The 1st time I had no solutions other than to trap the fox and get rid of it. I know foxes are not turned off by additional fox urine, dog urine, presence of dogs, people being around, and so on. The area this guy lives in is not coyote infested, so the fox may not know what a coyote is and be scared of coyote urine. I assume it is residential and he can't just shoot the fox.
Here's what he sent me on a MD gun forum:
I have seen your post on here and noticed you are a trapper and have a quick question about a fox in my yard.
We have had a fox pooping all over our yard for about the last 2 months, any home remedies that might chase him a way? We have tried some of the sprays from Home Depot but have not had much success.