At Lowes and Home depot they sell a few products which work pretty well from what I hear. It works for Cats, Moles, Squirrels, rabbits and more.
I can not think of the name off hand but it is in the insect repellant section by the sensor like things ya plug in the wall
Here we have many many squirrels running around but they never mess with our plants, But then if they did dh would just have them for supper
