Google for scarecrow and buy one of the motion activated sprayers. I used
one for a few weeks and found that cats learnt not to come into the garden.
Our major problem though was badgers and herons and it cured them! It
sprayed me a few times as well when I forgot to turn it off!! Nowadays, I
use it when needed

Perhaps you and a few of your friends/neighbours who have a similar problem
should club together and buy one. Used for a few weeks now and then and all
will be pleased.

Geoff