Hi wiggle,
Such brave squirrels! I've known a few to turn around and square up to my dog!!
I recommend putting some deterrents in your garden, they are repelled by similar scents to deer so you could buy some deer repellent and spread it around, use coffee grounds and even dog hair if you have a willing volunteer to brush!
Squirrels also loathe the smell of mint so you could plant some of these around their entrances to discourage them. Finally if you have some time to go and find where they hide their food (if in your garden) you could dig it up and relocate it.
using a mixture of these should begin to deter them and with persistence hopefully they will move on and leave you and your cat in peace!!
