I don't see that many movies with John Derek though he was in a number of them. From looking at the list of his work on the IMDb I can't see anything there that I have already. I picked up Rogues Of Sherwood Forest for pretty cheap used along with The Prince Of Thieves that I had watched the other day.
Rogues Of Sherwood Forest is a 1950 movie and it's directed by Gordon Douglas. Ralph Gilbert Bettison wrote the story and George Bruce wrote the screenplay. Ralph wrote 18 films in his 26 year career and the only one that stands out is the 1956 version of 1984. George wrote over 30 films and oodles of TV episodes in a career that lasted from 1937 to 1963. I've seen his The Man In The Iron Mask, The Son Of Monte Cristo, Kit Carson, The Corsican Brothers and a few more. His 1952 screenplay, with Harry Essex, for Kansas City Confidential is top notice. Well worth seeking out.
John Derek plays the son of Robin Hood. He regroups his father's Merry Men when King John gets too heavy handed with the taxes. They rob from the King and give to the poor. George Macready plays King John and Diana Lynn plays Lady Marianne. The MM beat down the evil rich twat and things get back to normal. There's the usual fighting with swords, shooting arrows into King John's pincushions men, chases through the forest on horseback and a bit of romance. It's an OK bit of fun but not much better than the 5.4 it scores on the IMDb. You can check it out on Dailymotion to see if you like it. The page you land on has some other 1950s adventure type films that might be worth checking out also.