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Woofy thanks. The owner doesn't care what his cat does. When I told him what she was doing and asked him to put a quick release bell collar on her he refused saying, "it's what cats do".
My little chap is not much bigger than the cat. She knows he can't jump very high and leaps just out of his reach then sits watching him, little madam. I have the usual high fence all round my garden but the cat lives next door and sits on top of the shed which is in its garden but against my fence. I have an arbour on my side covered in roses and honeysuckle. Yesterday my dog spotted her on top of it, crouched ready to leap onto a bird in the bird bath. Another flat owner has the same problem with her and another has seen her bullying a sweet little ginger cat that sits quietly on the front wall waiting for a stroke from any passer by. I'm afraid only the owner likes this cat.