What is your most effective squirrel deterrent?

Lay hot pepper flake around the yard. That deters them from hanging around!

Also, don't feed the birds! If there is no food source, they may go elsewhere.

spray peppermint oil, they hate it, they won't even go up the tree if it is arouond the bottom, lol

Mix Cayenne pepper to your bird seed, if that's your issue....the birds will feed, but not the squirrels.

Feed them away from any area that you have planted, a satisfied squirrel should leave plants alone. If you have birdfeeders, keep them away from your garden. They will clean up some of the dropped seeds and you could possibly leave food for them, like nuts and corn under that area and they will start going there for their meals. If all else fails, a mouse trap baited with peanut butter will scare them to death and they will leave that area alone. I did this with my half barrel planters, only put one trap out in one planter, didn't catch him, but never saw damage in either planter for weeks.