I am not much help on that. But I have read threads that someone had a bucket of water design that is basically a trap that the rats fall into and drowns. I will see if I can find it and post a link if you are interested in trying it.
Until May this year I had two Red Jungle Fowl roosters. I had them in my garage at night and then let them out in the back yard from morning until dark. One was called Rusty and the other was Oreo.
I was new at this and did not realize that having chickens also means bringing in other uninvited guest such as rats. Fortunately, I only had one male rat, that I called "Rudy" invade my house and lived under the concrete slab where the air condition unit was and eventually chewed a hole large enough for him to enter the wall of the house where the A/C line entered and then decided to move into his "private penthouse" in the attic. Then coming out only when I fed the roosters.
I watched Rudy from the kitchen window and noticed how brave he had become to venture out in the morning and steal all the food for the chickens. So I studied his habits and kept a mental note that I cannot use poison, nor a "snap" rat trap since either one could kill my birds.
I noticed the time of day how long he stayed out as well as what he liked to eat. Rudy ate everything, leaving nothing behind, but his favorite was Mr. Peanut’s big Virginian style nuts. The problem was that Rusty and Oreo also liked peanuts and since I had crushed them up, sometime the sparrows would eat the remaining.
So I had to devise a strategy to catch Rudy, without harming anything else, meanwhile, Rudy would keep me awake with is "partying" upstairs in the attic and living the good life, a roof over his head, all the food he wanted and not a worry in life except for the lack of females. Rusty and Oreo meanwhile were complaining about not having any food at the window walking with their banners back and forth in front the back door.
Then after I had thought about this enough, I went to my local feed store in Pasadena and found a cage type rat trap that would snap shut after the victim would enter. It was too small for the roosters, but large enough for Rudy. So after watching Rudy carefully, I placed in front of the exit hole at the concrete slab with bricks partially blocking the sides so that the sparrows would not trip the platform inside. Baited the trap with some very delicious "freshly roasted" peanuts and then waited.
Rudy came out of the A/C hole in the wall and could not enter directly because of the bricks, but instead went in underneath the slab until reaching the exit. For Rudy, it happened too quickly, the peanut was simply just too tempting to pass up, and before he knew what happened, he was trapped.
At that point, Rusty and Oreo were curious at all the commotion Rudy was making and walked around the cage eyeing him accusingly of shop lifting, but when I came out Rudy was actually angry, hissing and chirping madly. I picked up the cage and put him in the trunk of my car and drove down about 25 miles to Lake Jackson and let him out at a rest stop in the country. I guess he became some hawk's dinner guess. But it sure was a relief to me to finally get rid of him.
At this stage in my life, I might add, that it’s not good to have a party animal share your home. I went up into the attic and threw out the disco ball, fired the DJ, the rooster picket line went away after a union local food re-negotiation. But, because of travel, I had to return both Rusty and Oreo back to the person who gave us the chickens when they were young. They finally came to a place where all of the rest of the population was Red Jungle Fowl, eventually meeting some of the hens. I miss them. They were just two wild and crazy birds that gave me an understanding on how lovable chickens can be even if they were Roosters.