If you read this far, then you probably have some of these problems already. So, remove the food supply. If it is a bird feeder, move it twenty or more feet from the house. Close or cover garbage cans, and if possible make them inaccessible. If you have a barbecue near the house, keep it clean and covered.
Squirrels have been know to eat the drippings and sometimes build a nest if they can get inside.
It doesn't take very long, sometimes just hours. Maybe the squirrels are digging in your garden, or flower pots. While you can't stop a squirrel from digging, you can discourage it. Use hardware cloth, a heavy metal screening with a half inch square grid, to place in the flower pot. Cut it to fit around the stem of the plant, and extend it to the edges of the pot.