If shooting, trapping or poisoning is not an option then an aggressive dog, properly designed electric fence, netting or squirrel baffle can work.
@alan knows how to do the squirrel baffle. It will work for raccoons also. In addition to preventing them from climbing there cannot be any nearby objects that they can jump from. Also lowest branches should be 5 ft from ground. DIY Squirrel Baffle ideas? - #3 by clarkinks
Strong netting can work although putting on and taking it off each year is not fun. Also a squirrel can chew through it if determined.
For very dwarf fruit trees and low growing berries like blueberries a screen house structure will work. Use heavy duty screening like 1/2 wire mesh. Do a google search “blueberry screen enclosure” for ideas.