Human contact with cat faeces can result in the contracting of various diseases, one of the most common being toxoplasmosis. Cats that poo in the neighbour's flowerbed or a child's sandpit can quite rightly be deemed pests.

The symptoms of toxoplasmosis (akin to flu symptoms) include various aches and pains, a slightly raised temperature and enlarged lymph glands. In most cases people are not aware that they have got toxoplasmosis and get better within a few weeks.

Neighbours' cats can be a real problem for the gardener, as I know from bitter experience. From what I have read I get the impression that the most common problem they cause is in scratching up seed beds and areas containing young plants, apparently in covering up deposits they have left. I have not experienced quite the same thing, mainly because the untrained cats (they can be trained always to use a provided sand tray) in our area don't bother with covering up the mess - they do it on bare soil, on the lawn and on top of plants such as heather, and then simply walk away.

A second problem is that they will hunt, often successfully, almost anything small that moves, such as birds, frogs, etc. If mice or rats are a problem this can be an advantage, but if you try to encourage birds, or hope frogs will help keep down your slugs, then the continual visits of hunting cats are highly undesirable. Even if not hunting, their presence will frighten birds away.

I have come across many supposed remedies, most of which I tried and found to be useless. Two I did not try because the cure seemed as bad as the disease were keeping a dog and keeping a cat of my own.

Recommended methods relying on smell included bits of orange peel, moth balls and green crystals manufactured and sold for the purpose - none had any noticeable effect on our local felines.

I was told that leaving a few large plastic bottles on their sides half filled with water would deter the cats because of the strange reflections in them - but I found the bottles placed in common cat pathways quickly became crushed by the weight of the cats walking over them as they entered the garden.

Cocoa shell mulch was recommended on the grounds that it is uncomfortable for them to walk on (it is supposed to repel slugs and snails similarly) - I found they selected the areas covered with it to use for toilet purposes in preference to other areas, and it also failed to deter slugs, although I would still recommend it as a simple mulch. It is excellent at keeping down weeds.

Both a catapult and a large water pistol caused them to run off in a panic, but it did nothing to deter them from returning - they simply learnt to flee as soon as they heard my hand touch the inside door knob.

This leaves the one method I have more recently tried which, so far, does work. This is an electronic device which uses infra-red to detect movement and then emits a sound outside the range of human hearing but intolerable to a cat. It does them no harm, but they quickly learn to avoid the area where it operates. After years of frustration, my garden at last appears to be virtually a cat-free zone. Long may it continue! It is claimed that the device has no effect on birds, dogs or other animals - this is certainly true so far as birds are concerned, and I have watched a local hedgehog trigger it but totally ignore it. It can be powered by either a 9 volt battery or via an adaptor by mains electricity. Mine are battery powered, but I find they run down rather fast when they are frequently triggered by birds feeding regularly in front of them or by shrubs in front of them waving in the wind.

http://homepages.nildram.co.uk/~jimella/pests.htm