maybe consider wiping a bit of peanut butter or tuna along the ladder (enough to follow aroma) to encourage the rats to the bucket top, there to find the same actual bait, and then fall in.
I too discovered tunnels everywhere this year.. I'm a newbie w 2022 my 2nd winter tending chickens and I only have 3 hens. I've seen the tunnels under/into my garage, outside chicken pen, garden beds and compost! Then I saw several rats in my garage (where my smaller, Fort Knox nighttime coop is...