You don't keep a git repo in a synchronized folder (Dropbox, SkyDrive, ...): too many files, too many corruption possibilities.
What you keep is a bundle:
- one file
- which can be incrementally updated,
- and which represents your git repo
- and from which you can clone a local repo
See:
- "Git with Dropbox"
- "Using Dropbox to synchronize files and having them backed up in version control"
- "Git with Dropbox Issues"
Or, you can push those repos to a private repo hosting service like BitBucket, as commented by ta.speot.is.