So how can I avoid a minor character, from whose point of view the story is being told, becoming the protagonist instead of the person whose story I want to tell?
Well, you can't. Not really. The second it's written, the world will come to it's own conclusions. Like with The Tales of Sherlock Holmes. It's all told from the perspective of Wattson, but it's about Sherlock. So it can be argued that Wattson is the protagonist, or that he's just the placeholder of the reader. It's all about perspective.
What is useful to know, is that this narrative (told from the point of view of the sidekick) is far more common in Japanese media, because that is the common zeitgeist of their culture. The emphasis isn't on 'me' (broadly speaking), it's on 'us'. It's about cooperation, about uniting our focus to achieve a common goal.
So if you take stories like Final Fantasy X, where the story is effectively told from Tidus's point of view. Who's the real protagonist? History will recall Yuna as the hero. History at the time of the telling portrays Auron as the 'legend', being Braska's guardian that brought the previous calm.
But in the end, as is the common thread of the whole tale: "This is my story." Auron says that to Tidus. Tidus says that to Yuna. And Yuna herself comes to believe in the simple idea. This is my story. To me, this gives the viewer (reader, consumer) a sense of sonder--that everyone in the world crafted has their own story. And that might well spill out into the person's lived reality, where the sense of sonder lingers long after the game is turned off.
So. How do you ensure that your point of view character isn't the protag? Well, here are some thoughts on that.
- Make the point of view character bland.
By making the point of view character uninteresting, the person they are focused on becomes far more interesting by contrast. Again, look at Sherlock Holmes. What can you really tell me about Wattson? Holmes was intelligent, methodical, a master at hand-to-hand combat, fell into a depression after solving each case. But what was Holmes really like? I can't remember, because he didn't stand out.
- Offer the protagonist more screen time, even if written from 1st person.
While it's a bit... stalkerish if the point of view character's whole world revolves around the protagonist, it is incredibly potent if done well. Let's take Tomoko from Card Captor Sakura. She was in love with Sakura (I don't care what you have to say! Fight me!), and her whole world revolved around her as a consequence. She was constantly videotaping Sakura's life, following her everywhere. And when she got home, she would go through all the footage again.
Another option would be as you describe. This is a VIP's body guard. So have them methodically plot how to keep their client (or whatever) safe. Check the mail, check the car, check the locations the VIP needs to go to. Make exit plans. Keep close to them. Overhear the conversations--whether intentional or not.
In this context, it still feels stalkerish, but it makes perfect sense. But then you get into a very different thing. When the VIP isn't out in the world. What does the body guards see? When they are looking at the news broadcasts about the VIP, how does the world see this imperfect being the body guard is charged with keeping alive?
If you follow this route, it's perfectly understandable that the body guard needs to keep an eye on all aspects of the VIP. But you also get the advantage of them being snippy about it.
"Christ. I can't believe that woman's just up and vanished! What is wrong with her! Why hire me to keep her safe, if she's just going to up and leave whenever she damn well pleases?!"