Did you try any rat poison like this. I was check few rat poison and find this one.
https://www.amazon.com/Motomco-Tomcat-Weather-Chunx
I am thinking to buy this because this poison have lots of review on amazon. Definitely, I will test it.
Today, I was searching for the best rat poison and find this old thread. Actually, I have used a couple of poison (purchased from a local shop). This didn't work for me. These rats size is bigger than normal size. Thus, I need some powerful poison suggestion. What type poison are working great...