The third element of wildlife gardening is cover. Animals are more likely to stay around if they feel safe, and to feel safe, they need places to hide. Prey animals particularly want safe havens where they can retreat if they feel threatened. Predators, too, including toads, lizards, and garter snakes needs a place to hide as they hunt, rest, and escape from their own predators.
Ground cover provides living cover for many small animals. Insects, including many ground beetles, hide under thick vegetation. I've seen patches of ivy where garter snakes thrived, safely hidden by the thick leaves while moving freely between the vines and eating up the slugs they found there. A variety of different ground covers will give animals a choice of the green cover they prefer. Depending on the sun exposure of your site, consider Lady's Mantle, vinca, creeping phlox, creeping thyme, Roman chamomile, verbena, veronica, and evergreen ferns such as sword fern planted thickly. Be cautious of ivy, which has become a noxious weed in many forests. Ajuga, also called bugle, can also make a pest of itself.
Evergreen shrubs, both broad-leafed and coniferous, provide year-around cover for small birds. Clip them loosely so that there is good protection, but so that the shrubs are still open enough for birds to easily get in and out of them.
Brush piles also make great cover for birds and small mammals. Find a quiet corner of your yard where the pile will seldom be disturbed, and that's not directly in your line of sight since a brush pile can look messy. Lay down some logs, thick branches, or scrap lumber to provide open space under the pile. Then when you prune your shrubs, pile up the twigs and branches until you have a stack that is several feet high. If you have them, fern fronds or cedar branches laid over the top help provide a little rain protection.
Log piles, too, will provide hiding places for many small animals. If you stack wood outdoors for the winter, keep an eye out for salamanders and many beetles and spiders that will hide there.
Rock piles are favored by reptiles. Stack heavy rocks in a sunny place, preferably near a concrete sidewalk, driveway, or patio. Reptiles like to bask on the warm concrete, and can retreat to the rock pile if danger threatens. A few flat stones beside the pile also provide a basking place, as does the pile itself. Be sure the stones are heavy enough that predators such as raccoons would have a difficult time pulling your rock pile apart.
Roosting boxes are useful for birds in the winter when the weather turns foul. Cornell has a good site on birds with instructions on How to Build a Roost Box. Bats, too, use roost boxes all through the year. The boxes should be places on the side of a house, high wall, or barn, at least ten feet above the ground. They can also be placed on the side of a tree if the trunk is clear of branches up to and somewhat above the roost box, but bats seem less inclined to use a tree-mounted box than a wall-mounted box. Be sure, though, that the box is placed where bat droppings won't be a problem. Here is a site that has several plans for building bat houses.
One thing to keep in mind as you make your plans, though, is to have little cover near bird feeders and bird houses. Birds feel safer if the ground near their feeding stations is open, with few places for predators to hide.
For your own safety, be aware that lots of thick shrubbery next to your house can give burglars a place to hide. People living in poisonous snake territory may want to limit the amount of ground cover they grow, and keep the lower branches of shrubs trimmed up to limit the places where poisonous snakes might lurk.
The entire Gardening for Wildlife series:
Gardening for Wildlife: The 4 Element
Gardening for Wildlife: Food
Gardening for Wildlife: Water
Gardening for Wildlife: Cover
Gardening for Wildlife: Nesting Sites