For years I've been using plastic forks and spoons in my newly planted seed beds with great results: no cat digging! George runs along the edge of the bed but not through it.
The little seedlings come up between the plastic ware with no trouble and the guardians of the garden can be reused year after year.
This year I found a box of used bottle caps when I ran out of forks. So far, they're working just as well in keeping the cats sidelined.
