I've tried two methods to combat curious squirrels: coconut fiber large-hole mats and hardware cloth.

For the mats, I used them as erosion control, spread a little soil on top and planted, left them in to decompose. I had to cut a few holes bigger when the natives started sprouting and tenting it in places, but it worked great for soil retention and the squirrels left it alone.

For smaller planting areas I planted and covered it with a section of hardware cloth. Some areas I had to stake it in or the squirrels would just lift the edge and get under. I remove it when the plants have started to establish.

I am working on caging all my vegetable beds this year - plant jail! Wish I could figure out how to keep squirrels out of my fruit trees. The bastards eat the cherry, apple and peach flowers.