Just to follow up on Chuck's comment. Urine will have no effect whatsoever on urban foxes. It does however deter wild foxes, but only during daylight hours. They are not stupid and know humans are not nocturnal. We have been using it since the first daytime fox visit (recommended by a gamekeeper of longstanding), but only along the boundary with the gap in the wall, which is only 4' at one point, 6' the rest. We've never had a fox during the daytime since, but a regular visit of a big one at night. It just walks all round the coops looking for an opening- no change of pace, because I've seen the footprints in the snow- then leaves where it came in the gap in the wall.
This attack was the result of an entry 50 yards away through a bramble, over chicken wire, down the canal bank and through the only small gap in the fence. We didn't think a fox could get through, so had only guarded against rabbits. There was no urine spread within 50 yards of that point. In Summer that was used as the 'relief' point, which may be why the attack wasn't earlier in the year.