When we live in a subdivision, we can be surrounded by cats permanently which come to walk on our ground. We then have the bad surprise to see that they have urinated everywhere, left some excrement. Most of them are not castrated of course. This is a real problem because the smell of their urine is unbearable. Plus you can have a family member who is allergic to cat hair, so it is vital to find a cure pretty quickly.
An effective way to permanently repel cats is to install a solar ultrasonic repellent. It emits infrasounds that will scare not only cats, but all other animals, be it birds, squirrels, dogs, and other wildlife. There is four modes of frequency to repel only one type of animal, it is very useful if we have a dog or if we do not want to disturb that of the neighbor.
You can hang it on a wall, put it in the middle of the lawn, attach it to a pole. It has a solar panel, so it is not useful to recharge the device manually (unless there is bad weather) or to connect it to the electricity sector. It can be used to keep animals away from a field, a garden, a porch, a grove of flowers.