Probably quite a difficult combination to manage. Food attracts foxes (and just about everything else... including badgers, hedgehogs, cats, mice and rats). And as mentioned on other threads, poisons can enter the food chain, so putting poison down and attracting foxes that may predate the rats could misfire quite badly.
If you do try to attract foxes, keep food amounts small and try to monitor what is taking it. Foxes can become quite regular and so you can time when you leave it (and remove it if they don't show or you suspect rats). Dog food, scraps (not cooked bones), sultanas, eggs (though the shells are favoured by rats) all do fine.
Rural foxes will mainly be hunting smaller mammals, birds and (if your area is anything like mine) rabbits. They'll also forage worms, bugs, fruits etc. so they don't need the food as such, but I do appreciate wanting to see them up close.
Here's a rural fox in its element.. a bit like a trip down to the local supermarket