I feel I've been misunderstood and want to make sure my position is
clear.
I had cats marking in my garage, patio, and bushes. They made things
smell and die and drove my inside dog crazy.
I researched and tried everything from shooing them to throwing a
tennis ball at them to Tabasco or cayenne pepper on the ground to water
spraying to traps to neighborhood notes to talking with owners. My
talk with owners resulted in exactly what my research showed: they
suddenly didn't like me and they did nothing about the problem. I was
nice, explaining about my dying bushes and smelly patio. I simply
asked if they thought we could do something about it. They said you
can't rein in a cat. That's true. If you let a cat outside, it will
wander around.
My local laws make it illegal for a dog or cat to be off its owner's
property without a leash or the owner's full command.
Only two things worked to keep cats out of my yard. The first worked
only partially. It was a trap from the humane society. It worked on
only one cat. The cat had no tags (another illegality). The humane
society said they would keep the cat for seven days for an owner to
claim it. Then it would be up for adoption for seven days. Then it
would be put down. The owner did not claim it. My research showed
this is typical.
The only other thing that worked to keep cats out of my yard worked
100% of the time. I shot them with a BB gun. It's legal to shoot BB
guns in my city. I shot the cats far enough away so as to not caused
injury other than a bruise, and away from the eyes and ears to prevent
blindness or deafness. I don't know whether it's legal to hit cats in
my city. I bet it is okay. After all, pinging or bruising a cat with
a BB is no more injurious than spanking. And people spank their cats
(although the usually punishment is a finger flick to the nose) all the
time with no outrage.