Not too sure what the laws are here in Montana on game retrieve, but I do know that a homeowner DOES NOT need to post his land to keep tresspassers out as it is a persons responsibility to know where they are at all times while hunting/hiking. ect.
I live lin the middle of the Kootenai National Forest and my kabin is surrounded by forest, it is absolutely impossible to visit me without one tresspassing on my property, its pretty much remote but if a tresspasser were on my property looking for a deer that he had just shot, I guess it would depend on the individual(s) attitude. How in the hell could I ever deney a eager young hunter in persuit of his first deer?
But I will tell you one thing and that is if you came on my property and " TOLD" me your going to retrieve a deer that you just shot, you would have a serious problem and I would make you leave.
If in doubt, don' t ever take a weapon on private property, even in game retriveal.
Leave it at the gate/fence. ect.
Like the others have said, state/provincial laws are all different, so to be on the safe side and cheque with the local regs. Good Luck, Bobby