Apart from leaving log piles & leaves around for them you can put food & water out for hedgehogs too, you can buy special hedgehog food or use cat food (not fishy though), if you use cat food though you might end up just attracting all the local moggies. We have hedgehogs, usually only one or two which I nearly trip over at night when I'm picking snails off the plants by torchlight, but I haven't seen any yet this year. They like gardens with plenty of undergrowth they can hide in & as Alice says you need to have little gaps under your gates or fences that they can squeeze under.

__________________
Into every life a little rain must fall.