The scent that the squirrels hate the most is peppermint.
You can use some peppermint oil on some cotton balls and place the peppermint oil soaked cotton balls near areas that you want to repel squirrels.
Peppermint Plants are also good at repelling squirrels so you could plant peppermint plants near areas that you want to keep squirrels away from.
Squirrels also hate moth balls so putting moth balls in areas to repel squirrels will work as well.
Be sure to use some metal mesh to seal off areas where squirrels may be getting into your house or other places through.
But using peppermint oil or peppermint plants as well as moth balls can keep squirrels away or you can also use motion activated sprinklers that will spray the squirrels when they get near the motion activated sensor and eventually the squirrels will stay away.