Modern rodenticides are specially designed chemicals that cause vermin death by altering vermin's metabolism. One often used group of such chemicals is called anticoagulants. No symptoms are displayed by a vermin earlier than several days after eating the rodenticide loaded bait for the first time. The vermin can eat and digest several food intakes before it develops the first symptoms. Then the vermin starts being disoriented and becomes easy prey for cats and the concentration of rodenticide in the vermin body can be enough to kill a cat.
What's the typical approach to this problem except abstaining from rodenticide use (which is hard to expect from the whole neighborhood) and keeping the cats shut home?