When it comes to wearing butt plugs in public, I have had anxiety issues associated with it slipping out. So needless to say, I can't stand wearing them outside of the house without some form of guaranteeing my butt plug to stay secure. Mistress started having me wear snug-fitting pairs of panties and thongs to address the issue and it has yet to fail (although there have been some close calls, particularly thanks to a good cough or sneeze!).
Eventually, my Mistress decided to invest in a butt plug harness to keep me securely plugged. My harness is also lockable, which my Mistress absolutely loves because it adds a factor of security outside of my own control. Regardless of whether you are into the control/security factor or not, I *highly* recommend every butt plug aficionado to consider purchasing a harness, even for solo plug lovers. I'll gladly share some suggestions brands and styles if anyone's interested enough to send a message my way ;D