Can Sourcetree or Bitbucket prevent merging develop into a local branch?

[Mike Purrington]

Is there a setting or hack to configure Sourcetree to not allow the client to merge the Develop branch into a local working branch?  We have an ongoing issue with developers "tainting" their local branch by pulling the Develop branch into it mid-cycle.  Ideally, I'd like to make it so that the Develop branch is locked and the only thing you can do is branch it. 

FWIW - Bitbucket is our repository - but I suspect this is outside the realm of the repository since the method it uses to enforce pull requests is by preventing pushes, which wouldn't be possible for a working branch.