Hi Syd and all,
I had the same problem here and consulted the local council about it. It
might be worth contacting your local council as first point of call because
many councils these days do have regulations about wandering cats. The
council's ranger said that you had to try to notify the offending cat's
owners, if possible, in writing. If the problem persisted the council could
then loan me a cat trap and they would deal with it. This meant if the cat
wasn't registered, as they are supposed to be, and had no way of contacting
owners(micro chip, etc.) the cat would be destroyed by the council.
I tried this technique with my neighbors and with my first approach to them
the stunned neighbor was astonished to discover that cats weren't 'native'
Australian fauna. He didn't do anything, except stop feeding the cat when a
baby human joined their family, so it went feral and a neighbor a bit
further away started feeding it, so it spent less time in my garden.
We did catch one cat with a trap, but not the one I was after. The ranger
thought it was someone's pet, but as there was no way to find out who's she
took it away and, I presume, it was destroyed.
Eventually most of the neighbor's cats died and weren't replaced or moved
away. I now have a cat of my own which is kept indoors with limited access
to outdoors via a cage/run. She lets me know if another cat is around, but
there doesn't seem to be as many.
I'm not sure this is much help, Syd, but perhaps you should check with your
local council first to see what their recommended strategies are.