have (got) (someone's) back
To be willing and prepared to help or defend someone; to look out for someone in case they need assistance. Don't worry about those thugs, buddy. I've got your back if they ever come bother you again. You can always rely on your parents to have your back.
have someone back
to invite someone for a return visit. We would love to have you back sometime. We want to have you back the next time you are in town.
have got (someone's) back
To be prepared or ready to support or vouch for someone, as in a crisis.