Ooh, what a worry for you. I had an 'orrible experience with a rat in the spring. Neighbour had been feeding them! They'd obviously bred and were foraging for food around our overflowing wheelie bins (fortnightly collections AND I have a 1/2 size bin because I am a single person). I went to take the bin down the drive in the dark in prep for the morning collection. Obviously a rat had got into the partially open bin to get at the food and it jumped out as I was wheeling the bin and I just rolled the heavy bin over it's poor little body because I didn't see it in the dark. I felt like **** for weeks.
I think you're doing the best thing putting poison down, as sad as it is. Unfortunately the increased rat population is causing them to become more aggressive in order to secure food, territory etc. I believe they are aggressive towards guinea pigs and rabbits. Perhaps someone knows how to rat proof outside hutches? I guess you have to do that for chicken and duck runs too.