I have read that sprinklering cayane pepper powder around your yard will drive them nuts. Squirrels as they move forward into your territory use their smelling power and nose! pepper gets to their noses and you will see then hurl off quick.
Does not hurt to try. keep some handy at all times, out of areas where kids play, and its cheap.
For my heirloom tomatoes, I got poison wheet, as tomatoes get big, I put wheet in a tamperproof box (to keep kids and dogs away). Its funny, last week when I went to refill the box, I found Acorn inside it. Poor thing had left behind its Acorn in preference for poisoned wheet! Yikes! God bless that one!
I think this evening I might go sprinkle some cayenne pepper directly onto the mangos in my trees. They are close to being ripe and the squirrels are making me more and more nervous. Recently they've been devastating my Jamaica cherry tree (Muntingia calabura). My mango trees are small so the fruits are within easy reach. I'll also hang a couple ammonia-soaked rags from the tree. Lysol is ammonia, right? the problem is the Lysol I have at home is lemon scented - might actually draw the squirrels in, haha.
Lysol is not ammonia; cheap ($6 / gallon) ammonia is usually available at supermarkets. Ammonia is pure nitrogen fertilizer for plants, so I would not recommend putting any directly on the plants or you'll over-fertilize and poison them quickly. I usually take an old rag, wrap it around a large rock to prevent wind from blowing it away, and put that in a plastic container, then pour 1/4 cup of ammonia on the rag, and place the container near your plants. 3 such containers seem to keep raccoons out of my 50'x100' back yard, as long as I remember to add a little more ammonia every couple days. I do make sure to not let rain overflow the containers, as pouring ammonia on the ground will poison anything with roots there.
Hot pepper powder works OK until it blows away, which is a constant problem in Colorado. I've also accidentally disturbed and subsequently inhaled hot pepper powder I put out for the critters before; that isn't pleasant on the eyes, nose, throat or lungs.
Hot pepper juice applied to things will still aggravate the squirrels and make them leave; it gets through the skin on their paws even if they don't eat anything it has been sprayed on. Rain washes it off though and it requires re-application. I make my own by throwing some habanero peppers in a blender with a little water (DO NOT INHALE THE FUMES FROM THIS! I would suggest doing it outside) and straining the result. You can add vinegar as a preservative so it doesn't spoil while you're waiting to use it. If you get any juice on your skin, you'll experience the same sensation the squirrels will, so be careful! I still think it is safer than poisons though.
But even better than applying the hot pepper powder or juice to your plants or yard is to apply it directly to the offending rodents. I used to spray my fence with pepper juice and it would work for 2-3 weeks to keep squirrels out, but after spraying it directly on a squirrel or two, they and their friends seem to stay away from my yard for months.
Kevin