Let me add to the excellent post by
@cmom that rodents can become resistant to bait.
I'm currently finishing up a bucket of Tom Cat bait. It works but I recently found 4 fat mice that had set up housekeeping in my bait holder and were happily getting fat on the bait.
I ordered Ramik yesterday. I've used it before with good results.
About the holders. Make sure you can fasten them down so they cannot be carried off by a pet. I had a concrete block sitting on one to keep it from growing legs and a tail and walking away. My husband one morning found our Jack Russell/border collie mix girl dog in the pasture happily trying to chew her way into the trap. No idea how she got it out from under the concrete block but she did. What ensued was a call to a veterinary poison control center ran by the ASPCA who talked me through the whole ordeal. The treatment was oral peroxide which our dog was not thrilled about. It took me three ounces to get one ounce down her and the resulting volcano to make sure she hadn't ingested any poison. Gratefully she hadn't but she still had to take a weeks worth of vitamin K to prevent anything she didn't chuckup from hurting her.
We both learned a lesson. She doesn't show much interest in the bait holders and I now put them in my have a heart traps and my wire cage so she can't get them out and try to chew her way into them again.
Never under estimate the determination of a mouse loving dog or cat when it comes to handling bait. I won't even get into children and other such animals.
Also on a curiosity side of things. Do chickens eat poisoned mice? I've never seen my birds touch a dead by poison mouse. I've seen them chase down live mice resulting in me having to chase down the chicken involved and removing it from her beak but if my birds encounter a soon to be dead from poison mouse, they give out their alert danger danger call and make a wide circle around it. They can sense what is wrong, I swear! Last night I picked up a dead mouse in the bachelor run. Those boys are like Mikey, they will eat anything but they hadn't touched the mouse.
I wish our dogs were that smart!
As for humane and inhumane. Let's face it guys, death by poison isn't exactly an easy death either but it's us or them as the saying goes. As for rodent death by drowning...yeah, I've entered my coop to find a mouse swimming around their heated water dish in the winter. Do I rescue it? Nope. I turn away, get busy for a few minutes, then dump the victim and the water outside. No death is humane, nor is it humane for rats to chew the toes off of chicks or hens while they are asleep at night. They are vermin. Pure and simple. They spread disease and are the primary vector for Lyme carrying mice and Bubonic Plague.
Makes me wonder how many do a few laps in the water bowl for exercise and escape to breed another day....