Moonman2 writes:

I am having trouble with a cat that keeps fouling right next to my
house(10cm). To make matters worse there is an air brick vent there - I
am sure the smell is travelling into my house.

What do you mean?
Do you smell the cat poop inside the house or not?

Cats usually bury their poop.
You might not smell it and the cats eventually fill the space
and move on.