Thanks for all the responses. I think on reflection I'll hold off on
suggesting this idea to my neighbour. I'm not clear as to whether it is the
dog chasing the fox out of the garden or simply the dog's scent in the
garden that is effective. I had hoped the latter. I've also realised from
reading some of the replies that I could well end up exchanging one set of
problems for another. For example, the yellow spots in the lawn from dog
pee. At least the fox just flattens the grass. (Although the ornamental
grass we had in a large pot was so well flattened it never stood up again
afterwards.)

The references to the peacock and the foxgloves were good. They helped to
counteract some of the less welcome contributions.

Annette asked if we had tried Renardine. That's what we're using at
present, but it doesn't seem to make much of a difference. Possibly it
will last longer in drier weather conditions, but it seems a rather
expensive solution.

I have to admit that I'd consider the llama suggestion if I lived in the
country and had enough land.