There are many people who want to keep neighbours’ cats out of their backyard and there are many methods, some of which will fail. I like these two methods and I will recommend them as a starting point because they may fix the problem for you. Importantly they are humane and perhaps even more importantly from the cat’s perspective they are what you might call “divine intervention”. The cats cannot associate a particular person to the deterrent. It is just that something happens in the backyard which they don’t like and so they retreat and take themselves away from the area. They should also learn that the area i.e. your backyard is not a place for them to be. This is the objective.
Dr Bruce Fogle, a respected UK vet and author, recommends divine intervention. I think he first coined the phrase.
NOTE: Personally, I would not use these devices. I accept a cat coming into my backyard. It is okay for me but I respect the views of others. It is just that I don’t want cats to be hurt by irate non-cat owning neighbours.
Motion activated water sprayer
The device sprays water over a cat when it picks up the cat’s movements. It contains a motion sensor. As the device is operated automatically by the motion sensor there is no one there. It is an act of divine intervention from the cat’s perspective. The cat will not be harmed but deterred. It is a humane device and based upon Amazon reviews it is effective. It might not be 100% effective but I would hope that it was sufficiently effective to satisfy the purchaser.
Motion activated ultrasonic cat scarer
This is a very similar device which is also motion activated but rather than spraying water onto a cat it omits a high pitch sound which is barely audible to people but very audible to cats. The device is based upon the fact that domestic cats can hear frequencies much higher than people because their hearing is designed to pick up the sounds of mice for instance. Their hearing is particularly sensitive to these high-pitched sounds and they can locate mice accurately through sound. But as people can hardly hear it the device is unobtrusive to a person but a big put off to a cat. Once again, it’s a humane device and judging by the reviews it is satisfactorily effective. Some reviewers are effusive about its effectiveness what others are less enthusiastic.
Both the USA and the UK Amazon sells these devices. They stock an extensive range. In the UK Pestbye® is featured as a manufacturer. I don’t think this manufacturer supplies America but there will be alternatives.
For me, the important aspect of the devices that the cat simply relates to them as if they are objects to avoid. There are many objects to avoid in a cat’s life therefore it is nothing special in that regard but it is effective. It certainly beats more aggressive methods.
The best website listing the most extensive range of alternative ways of making a backyard or garden unattractive to cats is the WikiHow website. I rarely link to external websites but I will on this occasion. Please click here to read their article. They include such methods as mulching the garden, using concrete-reinforcing wire or chicken wire with 1 inch openings laid across paths that lead to your garden, using sticks or branches crisscrossed across your plant beds, placing spiked mats in the garden (plastic spikes that are uncomfortable for a cat to walk on), using an odour repellent, using citrus as cats do not like the smell of citrus, using other strong scents such as pipe tobacco or coffee, spreading crushed pepper on the garden, planting rue, making certain areas of your backyard attractive to cats by, for example, planting catnip which will keep cats away from those areas that you want to protect. This might also include putting down sand where trespassing cats can have a poop. This might sound peculiar but if you want to protect your garden from cat poop, making one area attractive for that activity will prevent other areas.
One last, perhaps excessive, measure would be to circumvent your backyard with a fence with a large overhang facing outwards. The entire yard or garden would be protected by a cat-proof barrier – total peace of mind.