I have just been reading this thread and think I will put in my .02c in.
I am a geologist, but I am not only at risk working in the bush. I find with the amount of time I spend outdoors gold panning, hiking, rock hounding, hunting, etc on my own personal time I am very vulnerable to attack from all kinds of critters. I carry rifles right now, but I often find them 10-20 feet away when I am gold panning, or doing any kind of labor related work. They are really just a pain and they end up being out of reach. I have bought an antique because it is my only means as a last line of defense against animals. I may have a cap and ball but I will tell you what, at under 15 feet away (which is where I would likely shoot an animal). I think it will pack enough punch with the right shot placement. Half of my reason to have a gun around is to scare the animal off before the situation gets too dangerous anyways (works most of the time). I would love to be able to carry a large caliber pistol all the time, but the laws don't allow it, so I took the next best thing. My plan B is always a pig sticker I have on my belt, but really any animal that has me on the ground more than likely will kill me if I am being realistic. They are much more powerful than any man, and evolution has made them deadly.
As far as holsters go, I have thought a lot about it, and I think a shoulder holster rig would be good, although I haven't tested it with my gear on. It would keep the pistol handy and out of the elements for the most part, and out of the way of any waist straps. The only problem would be in certain weather conditions when you have to wear coats. My second option would be a drop leg holster with a flap over top to prevent crud and rain getting into it.
I am still an avid proponent of bear spray, it may not work on all animals, but it has kept me alive so far. I have never had to shoot a rifle at an animal in self defence, but it only takes that one time in a thousand.
I was talking to a guy in Granlunds today, and he mentioned that Indian tactic of putting a mask on the back of your head so that predators think you can see them when they are behind you. I might actually give that a try gold panning. I often forget to check my surroundings regularly.
Go with a 'Tanker style' holster, you might find it quite workable.