I went around his back

At first blush, this sounds right but on closer inspection I think it’s a bona fide malaphor.  In an interview with Jimmy Kimmel, Jennifer Aniston said this one when she was talking about auditioning for a role on the soap opera in which her Dad was a regular cast member.   It’s a congruent conflation of “go behind (someone’s) back” and “go around”, both meaning to do something secretly or without your permission.  This subtle mashup required someone with the ears of a hawk and that would be none other than Mike Kovacs, a regular contributor to this website.  Thanks Mike!