Merchants - Protected by Military

[Slaists]

So you rationalize the fort as a trading post? Cool. Though that's more investment so it'd better be a worthwhile resource.

Well, the key here is "a double resource" in a province. A double resource camped by your faction's merchants will allow them to raise their skill fast through the monopolist/market controller line. Once they are above skill 5/6, they become hunters themselves or can more or less safely travel to high-yield resources on their own (a level 10 merchant does not have a high success chance in a takeover of a level 6 merchant).

So, I would see a couple forts on a double resource a "merchant training school": a good investment in the long run. Well, it would be more fun if I didn't have that nagging feeling this was an exploit actually :)