Re:
I'd just like to add that the concept of "ownership" is a broader category than it might appear to be on the surface. I guess we have all heard of General Custer? No doubt he had a revolver, which would be "Custer's revolver". I think he also had a moustache, which would be "Custer's moustache". He is mostly remembered for the "last stand", which would likewise be "Custer's last stand", even though it involved a lot of other people, some of whom were "Custer's troops".
I also just realised that there is a whole lot of present tense third-person singular verbs that end with an "s", and are thus ripe for apostrophe abuse. They do not need an apostrophe.
If, instead of making a last stand, Custer decides to surrender, or shoots himself, or shits in his pants, or even orders a take-away curry...
well.. apart from "his", all of the words in that sentence that end with an "s" are present tense third-person singular verbs, so none of them are going to need an apostrophe before their terminal "s".
But of course if Custer decides to surrender, that is Custer's decision.