This has not been a problem with my garden (my nemesis is the gopher) – and I’ve seen only one tree squirrel so far running along the telephone wire above my back yard, but it has been a significant problem with my friends’ backyards, whose crops have been reduced or completely destroyed by them. With any pest that threatens to destroy your crops, you may have to draw upon more than one method of abatement or management.
Here are some useful sites that describe multiple methods of tree squirrel abatement and management for various parts of the United States. Note that some states have regulations on the killing of tree squirrels. Contact your state officials at their respective department of game (or game and fish, etc.) on the specifics on what is permissible:
South Carolina: https://www.dnr.sc.gov/wildlife/publications/pdf/squirrel.pdf