I am going to ask advice of our county council authorities as they
offer a service for a
reasonable price

I'd be amazed if they didn't do it for free.

and I must protect the poison from the cat and the
dog, but
I would be interested to know if anyone has any positive evidence of
the effectiveness
of poison for rats.

Well, the council contractors will set traps that cannot be invaded by
pets. They'll also use an effective poison. Don't worry about it. Job done.

FWIW, when we had a minor rat 'issue' I found that BFO spinesnappers worked
reasonably well, bog standard 'blue' poisened grain worked very well, and
humane traps were a waste of time. Airgun was potentially vaible, but the
buggers kept hiding from me Didn't get chance to try the sticky mats as
I'd killed 'em all by other means before I had a chance

My advice? Council. Much as most gummint bodies are a waste of oxygen, the
environmental guys seem to be really on the ball.

Al.