From the Pound Shop/Wilkos etc. I buy hook-together lengths of hooped plastic-coated wire - they sell it in white or green. Rows of seeds have these laid either sides of the rows - then twiggy bits are interlaced between the hoops. When the plants are grown, they can then be removed, cos the cats don't p**p on or scratch the established plants?**
For larger broadcast areas I do as Tim does, raising the mesh on legs of kindling sticks until the plants are established.
** except in Glos, where the local cats used to scramble on to the top of hedges to do it there ??? ::)