I like to have a "Projects" directory where I keep all of my projects. Some of them are hosted publicly on github, some of them are private side projects. Instead of paying github to host private projects, I use Dropbox for free to backup my code securely.
I accomplish this with a symbolic link. I make the directory for the private directory in my Dropbox folder, and then in Terminal, I go to my local "Projects" directory and create a symlink to the Dropbox project directory:
ln -s ~/Dropbox/Projects/project_name project_name
I still use git to take advantage of version control, but now the code is automatically and privately backed up.