I live near a dead-end river, and have noticed that it's been getting some traffic lately. I then began to wonder if it'd be possible (or worthwhile) to simply blockade the river with a big line of boats and/or rafts left standing in the water. While I'm sure people could just hop out and carry their boat around the blockade, I do own the property on both sides of the river, so they'd either have to risk trespassing or take a long detour around my borders -- either way, the annoyance of such things might cause them to think again about river travel.
While I don't think it's something I'd want to actually try (the repercussions would likely end up with me being a dead n00b, as I think I'm the only property owner on or near this particular river), I am curious as to whether or not it'd actually be plausible and/or effective.