We are having continuing problems with another cat coming into our garden and attacking one of our cats. We've had 3 trips to the vets as a result in the last year. Not only is it expensive, we are concerned about our own cat's safety and health. The vet thinks the aggressive cat may be behaving this way because it is a male cat that hasn't been neutered. We think we know where it may be coming from, but of course cannot be sure. I suspect there is nothing we can do, but I have wondered whether it would be completely unreasonable to knock on the door and ask them to get their cat neutered! Has anyone found a way of deterring aggressive cats?