You can't really stop cats doing their business where they choose. One thing you could try is to "cat proof" your garden to keep them in yours & stop them going in your neighbours, if you wanted to. You can "do it yourself" if you're handy - attach inward facing braclets to the top of your fence & then attach mesh to the brackets - I think, lol!! You'd be able to get proper instructions on the net I'm sure!! My friend has got it in her garden & it's worked for her. Hope this helps!

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Mum to Saffy, Tilly, Sox, Mia and Munch