As woofgang suggests. Me and my next door neighbours had seen a rat in our gardens a couple of years ago. The Environmental health officer came around and immediately pointed out the back garden two doors away. They have a staffie type dog which is never walked the owners leave the piles of poo in the garden, which is like a tip. All the other gardens are lovely except theirs. The Officer immediately gave them a warning to clear up the mess and said that further checks would be made. She couldn't pinpoint where the rat came from. Eventually the neighbour got rid of the dog. No more problems.