I've just been using pure essential oil, like this one:
http://www.hollandandbarrett.com/pa...a Pure Essential Oil - MTE-_-[citronella oil]
Then I put a few drops of that and a few drops of lavender oil in to a plant misting spray thingy with some water then spray.
Although lately I have been putting it
neat on to cotton wool that I have tied round the kennel - someone else had suggested that and I thought it was a good idea.