Geoff Hamilton had a good idea for cloches, which one uses across 4 foot wide beds.
Buy a 25 metre roll of 25mm blue water pipe and three 8 foot lengths of 18mm dowel - hardwood to last.
The pipe is marked in metres. Cut it into 2 metre lengths and, if you want semicircular hoops, cut the dowel to 1 foot lengths.
Stick 3ins of the dowel in each end of the pipe and fix with 1½ inch screws through the pipe and dowel, leaving the head protruding ½ inch.
Push the other 9 inches of the dowel into the ground to provide a secure fixing for the hoop.
Fasten the plastic or net with string over the hoop, from screw to screw. You can then slide the cover up from either side.