A hedgehog and an univited guest too

I think we may have a problem here. As regular readers will know I "invite" hedgehogs into the garden by putting down bowls of water and scattering food (usually mealworms, sometimes peanuts) but now it seems another creature is taking advantage of the free meal and its not really the kind of creature you'd want to encourage. I'm not really sure how I can discourage the rats without also discouraging the hedgehogs. Any ideas?