One of the neighbouring cats desperately wants to be Urchin's friend. On one memorable morning he actually let her out of the cat flap (which was set to ingress only - he pushed it from the outside and she shot out). Unfortunately, she isn't having a bar of it. Her home is her castle.
Paul got this wonderful series of photos demonstrating how she sees him off.
After assessing the threat (and correctly judging it to be much smaller than her) she gets into slinky attack mode and starts nipping at his heels. It is possible she thinks she is a sheepdog.
She follows him right down to the back of the garden and doesn't come back until she is totally satisfied that he is gone.
Then she looks very smug about having defended her home. This is also how she looks when she has been protecting us from squirrels.