Why I hate my neighbours cat

I don't want to come across as anti-animal. Indeed I share my home with this lummox:

But I really, really hate our neighbours cat. It is white and fluffy and cr*ps all over our kitchen roof. We know this because we can see the flat roof of the kitchen extension from our bedroom window. It also leaves dead things on our garden path and digs up plants.

I have a dog who manages to keep the garden nice (he knows he would be out on his ear otherwise.) The dog also hates the cat and has nearly caught it twice.

I have asked at the local garden centre and they could only suggest some cat away spray that frankly is waste of time and money. Our new plan is to criss cross barbed wire over the roof so that should the cat feel the need to poop, he will feel the discomfort of the barbs instead and be, er, discouraged. This will also be an excellent burglar deterrent as well.

Is this cruel?