Anyway.............I shall retype my long lost post.
Had the same problem with rats living under the shed. Tried everything from poison to catching them in live traps and "baptising" them.
Nothing worked. They breed faster than you can kill them.
In the end I solved the problem by digging a trench 1 foot deep and the same distance out from the shed, all around the perimiter. Then attached strong steel mesh (£2 a sheet from The Range) to the outside lower edge of the shed and down into the trench. Bend it to 90 degrees at the bottom of the trench so it extends out to the far edge of the trench. Then fill the trench in with hardcore & gravel, with soil on top.
It was hard work, but was the only thing that succeeded where all else had failed.
Just like us, rats cant stand metal on their teeth , so wont try to gnaw through the mesh.