From Wikipedia the free encyclopedia, by MultiMedia
A cat deterrent is a mechanism or device used to discourage cats from entering an area, or to encourage them to leave if they do enter. Cat deterrents are most commonly used by gardeners, in order to prevent damage to their gardens or avoid acquiring unwanted cat faeces; people with an interest in observing garden birds also use cat deterrents.
Cat deterrents include:
Lion Dung has been reported to be an effective method of deterring cats, and has received support from the British organisation Cats Protection. Research reported by the BBC  found that it was not terribly effective however.
Cats dislike the smell of citrus, and citrus-based products are used by some as a deterrent.
Ultrasonic devices (inaudible to humans) are a popular method of deterring cats. The RSPB, on the basis of a trial involving 150 volunteers, has endorsed a commerical product called "CatWATCH" RSPB research on electronic cat deterrents
A design for an electric fence for deterring cats can be found here. A variety of commerically produced electric fences are also available, with voltages low enough to deter but not cause harm to cats. Care must be taken with the strength of electric current used; one Cumbria pensioner received a fine for setting up a system based on a 12v battery  .
Cats Protection describe the use of electric fences as "barbaric" on their website, though they do not give any evidence to support this view.
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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.