Some poisons are designed to kill and desiccate the carcass to reduce the time of smell. One bait for mice is cotton as the mice will try to remove it form traps for nesting. Something on this order might be interesting. You might be able to feed them some bait with an ultraviolet tracer or something to find a path to where they live.
There are rat problems in the White House, New York and other large cities. This would look like a business opportunity to train cats, snakes, what not to dispose of the rodents.
A 10 x 10 x 10 bird nest box with a 2.5 inch hole in it set up high will attract the pregnant rats, esp. if you put parrot pellets in it. Leave corn husks, wool, cotton, wads of soft paper or insulation around the area; the rats will gather them up and stuff them in the box for a nest.
As soon as you see this stuffing sticking out the hole you know it’s occupied. The entire family will sleep in there in the daytime. If you haven’t rigged the hole with a clear plastic lid on a screw for a pivot, Just slap some duct tape over the hole, trapping them inside the box.
Then drop the box in a tub of water and weight it down, they’ll drown, but leave them there and go to lunch because they don’t drown fast.
Dump them out, dry the box in the sun, reuse. I caught 44 in a day that way for someone who had a flea market booth. There was bulldozing going on in a neighboring field and the rats displaced from that invaded the market one summer.