In article ,
The Natural Philosopher wrote:

Best solution is not to have a food source.

No matter how many you trap new colonies will move in

Second best alternative is to get a terrier.

Thanks TNP -- "I knew that". A feline hunter is also good -- just the
knowledge that it's around is enough to keep the rats away. As is, in
my experience, the killing of the odd one in a trap.

See one in the garden in daylight: too many around. Kill a couple:
don't see them again for months. (Leave 'em alone: an invitation for
them to set up a settlement.)

Cheers
John