G'day,
Martin, if you are anywhere near Wingham, I'll have the dog.

Cristian, it might not be the perfect sollution, but Earth cats
are usually pretty easy. For starters you have to let the cat know it is not
welcome anywhere or anytime in your yard, (hissing , chasing, loud
clapping, throwing things, practising that 'Headmasters voice' , etc), You
can't be friendly with the cat in one circumstance, and then expect it to
stay out of your yard the next . Dogs are a good solution but they can bring
their own problems. Failing that then place mothsballs around the places you
want them to avoid or where they enter your garden, (If you can't place
whole 'balls' then crush them up with a hammer and put some dust around).
Considering how cheap mothsballs (napthaline) is, I can't imagine how they
farm and harvest them, but any animal with the nasal sensitivity of cats and
dogs simply finds them to painfull to stay anywhere near. Our (preferably
male) urine can be used to stake out your territory, (which is exactly what
your problem cat is doing), but if you ain't careful, the neighbours will
be talking about you. They basic rule is that any time you see the cat you
must act aggressive towards it. I love cats, but the simple fact of the
matter is they are an environmental disaster, killing all your small
reptiles and any bird they can, thus destroying most of your natural garden
pest controlling species. I grew up with 'mousers', but as good company as
they were, I will never own a cat again (as if anyone ever owned a cat, we
just were given the privilege of petting \ feeding them.).

China
Wingham
NSW