What is the best thing to use to get rid of annoying squirrels?

trap and release across a river.

trap and relocate across the river.......or relocate to stew pot depending on time of year.

Stick Mothballs in their tunnels, or near the shrubs that they love. They will go elsewhere.

cats

Have you tried using Ceyenne Pepper? You can sprinkle it on the ground and in the birdseed in your open birdfeeders....it will not hurt the birds and the squirrels do not like the taste of it and they leave...it works.

Get a bag of blood meal from the nursery, spread through garden. The squirrels don't like blood smell at all and it also is a mild fertilizer