Below is a quick video of what I installed on the 20GP side of the fence on the afternoon of Wed, Oct 6, 2021. It’s a start, and in no means going to solve the problem, but it will help and start to answer some questions.
I think that the obvious hole they have dug now has a good seal on it, but I’m sure they’ll try digging another route. I could move the brick and fill it in with water, but in case wet rats come running out the other end, I don’t want to do that before timing it with Joe and Cheryl.
To the right of the post, running towards the house is a different story. It’s got a clear way for the rats to go through. Before I seal it up I want to keep the camera on it for a night or two and see if they are running in and out of there. Once the hardware cloth is down, it will seal them from crossing between 20GP and 22GP through that gap but will make it much harder to film if they are getting inside of 20GP through the piping.