Walter Bradshaw wrote:

Yes! You can rid your garden of a cat forever if you precisely follow
my three point plan. I have employed the following method for nearly
thirty years with 100% success. No more useless ultrasonic 'cat
scarers', lion dung, carpet grippers, water pistols etc. And, more
importantly, no more bird-killing-vermin in your garden.

Here are the three steps:-

1 Trap

2 Drown

3 Repeat as necessary

The need for Step 3 demonstrates that your method is a complete failure
and can guarantee nothing (except perhaps for a certain sadistic
relish). I do note the careful wording of your claim, however, and have
to admit that you can indeed rid your garden of A cat, a particular
specified cat, forever by the means you advocate. The trouble is that
you have to keep on doing it to each specific cat, which is hardly a
solution to the general problem of feline incursion --until, I suppose,
the species becomes extinct as a result; quite a long-term plan.