I found a large piece of fishing net washed up on the shore and cut it up and laid it on all my beds (after they were prepared for sowing). The holes are 4" squares and it even helped with spacing out the seeds, onion sets etc.
Not only has it kept the cats away but I can let the hens free in the veg bed without any trouble, as they won't go where they can't scratch.
In my experience, cats want soft soil where they can bury their doings, as being crafty predators, they want to conceal their presence. They will always head for bare, freshly dug earth.