I have used pure peppermint essential oil before, we had a rat trying to set up residence near our house under some concrete. I've also read that urine (I believe male urine... it always seems to have to be male urine to send things packing!) is also effective, so I put some earth down the rat holes and access points, kept adding drops of peppermint oil in layers of earth and topped the whole thing off with a jug full or male urine provided by my other half!
I ended up having to chase the rats around the garden over a few weeks as they tried to move to various other parts, repeating the process for a while before they gave up. It works though!
Far, far better than the horrors of putting poison down. Even for those without any feeling of compassion for the nightmarish death of that poisoned animal, it's still only 'safe' to put poison down if you are able to recover the dead body otherwise there's a whole series of creatures being affected in the food chain. We found this out earlier this year when our dog found a poisoned rat in our garden. The dog was fine, she let me know there was something there but other animals aren't always so lucky.
May you stay rat free... albeit peppermint scented!