It seems to be pretty universal that people (in particular parents of young children) are not too happy about neighbourhood cats using their garden as the toilet (I’m sure most people wouldn’t be happy about the neighbourhood dogs using their garden as the toilet either). A garden covered with cat faeces which might contain Toxoplasma gondii (a parasite that causes neurological problems) is extremely incompatible with young children, who are drawn to dirt and fail to resist putting random things in their mouths and licking anything from a daffodil to a rake.
The only group of people that might not mind cats using their garden as the toilet are the cats’ owners. But paradoxically, cats tend to prefer their neighbours’ gardens to their own.
In Japan, catless people tackle this problem with PET bottles filled with water (see photo above). I’ve understood that the use of these is based on three assumptions.
1) Cats don’t like water. (I’m giggling just typing this silly argument!)
2) When a cat goes close to the bottle, they see their own reflection on the bottle, thinks it is another cat (probably a size of a tiger due to the bottle distorting their reflection) and consequently runs away. But cats are intelligent animals, they wouldn’t fall for this, would they!?
3) Maybe more convincingly, cats don’t like the prism that sunlight creates in the area surrounding the bottles.
I was going to suggest that instead of taking the drastic measure of buying a dog (or your own cat!) you, my non-Japanese catless reader, could use PET bottles instead, to make your garden less attractive to cats, but then it dawned on me that this would only work in places with lots of sunshine (e.g. the Sahara and Japan). Given that we have only about a week’s worth of sun per year in Finland (and even less in England), in these countries, the use of PET bottles would be as effective a cat deterrent as gluing a photo of a dog on your garden shed.