An ultrasonic cat repeller is a good investment.
When I moved into my current home, I had shrews living at the bottom of the garden, and toads in a patch of rough grass nearby. SOme local cat got industrious about killing them, leaving the corpses spread out on a flagstone for me to see. After that, I had to suffer a plague of slugs and snails for two years. I tried beer traps, but they had a minimal impression on my problem.
I have cultivated a small area of rough grass behind some shrubs for toads to live in (I've got a couple), and thrown some stones in a heap into rough land just over my fence, in hope of attracting slow worms.
Things are getting better, I have less slugs and snails. But I can definitely say that keeping cats away to start with is a good idea.