There are animal deterrents on the market that are sometimes helpful as long as you spray after every rain or sprinkler irrigation. Hot pepper spray is one (capsaicin is the active ingredient). Always read and follow the label instructions.
Remember, your goal is to "encourage" the squirrels to eat something else. So the success of any deterrent program is contingent on what the edible options are in the area. If this is unsuccessful, you will need to cover your plants with a secure 1/4" screening or greenhouse-like cover to prevent squirrel access.
For additional ideas, look at this site: www.icwdm.org.
