Hmm we have a big fence around the site, and it is locked. You must lock the gate after you when you come in and again when you leave. Each shed has a bolt, it is up to each one to decide whether or not to put a padlock on. MY OH insisted on a padlock, I can't see anyone pinching my old rubbish.
I think there is probably a case for the site to be fenced, it would seem wise to deter vandals and veg pinchers. But perhaps it depends where it is? In an urban area, that would make sense.