Squirrels are adaptable creatures and readily move into environments where food is abundant. Attics, chimneys and decks provide squirrels with secure locations for their dens, close to the easy meals provided in people's trashcans. The best time of year to try to get rid of squirrels under your deck is in the very early spring, before a mother gives birth to her litter or in the late fall when the mother's young are big enough to move on their own. It is much more difficult to get a mother and newborn young to relocate.
Place a bright light under your deck. A light equipped with a motion sensor is more effective, and a battery-operated rather than wired light prevents the squirrels from disabling the light by chewing through the wires.
Place ammonia-soaked rags under your deck. Place the rags in hole-punched plastic bags so the rags won't dry out. It also reduces the risk of the squirrels poisoning themselves by ingesting the ammonia.
Place a battery-operated radio tuned to a talk-radio station under your deck. Keep the radio on for at least three days and nights.
Attach steel mesh to any openings under your deck. Once you are confident the squirrels have left, bolt galvanized steel mesh to any possible entrance points preventing the squirrels from returning in the future.