The poisons don't really work now, anyway, because the rats have become immune to all of them, although not so much in the country. So all they represent is more food, and therefore encouragement. But in any case they are very inhumane and if the dead, dying or merely contaminated victim is eaten by another predator or scavenger, these too become victims (whether or not the rodent is effected).
The only really good way to control them - and it is an especially good method in the country - is to encourage owls. In particular Barn Owls. You can do this by building nesting platforms in old buildings, or by erecting a Barn Owl nesting box. This is essentially like a small dog kennel but about 20 - 30 feet up a tree. Leave a landing platform in front of quite a large entrance with about a four-inch plank across the bottom of the opening over which the owl will climb in from the platform.
They are relentlessly effective pest-controllers and spectacular to watch - quartering their territory, sometimes really close to the ground, like great white-brown moths.
They are also very territorial, so if you erect more than one box, and are lucky enough to attract an owl, remove the other boxes when it has made its choice, so as not to attract others which might disturb 'your' bird.
And don't forget, mice, rats and other rodents are a natural part of the country fauna, it is just plagues of them that are a problem, a 'healthy' (in both senses of the word) population is not a problem and is needed to sustain their predators - it is the absence of these latter, killed off by the use of various chemicals getting into their food (prey) which is what leads to the plagues.
Give it a try and good luck. (And as you say, keep clear of the poisons).