Secrets of a Super Stud, also known as It's Getting Harder All the Time and Naughty Girls on the Loose, is a 1976 British sex comedy film, one of many to be also filmed in a hardcore version for export. It was shot at Twickenham Film Studios under the title "Custer’s Thirteen", the general release prints and the hardcore version were processed at Kay Labs at Highbury, North London.

Details of the film's hardcore version were leaked by the magazine Cinema X (July 1976; vol.8. no5, page 22), after the magazine had become disillusioned by certain British filmmakers refusal to acknowledge they were shooting hardcore "at Cinema X magazine we know which directors have shot porno; we’ve talked to their stars. But its little use quoting them, when the directors, producers, above all their distributors, vociferously deny everything. We prefer honesty in our pages."