A More Grand Solution
Here is an expanded Success Grid that can be used when multiple people have to pool their strengths or skills to perform a task that a single character cannot. Moving a tree from across a path would be such a task.
To Roll or Not to Roll
To keep the players guessing, the AM can roll dice arbitrarily during play but not use the results. Always look at the dice or the players will eventually guess that you are just doing it to keep them in suspense. Check your charts or papers quickly to make it seem legit. This ruse works best when you are using an AM screen. I prefer a half-height one, the regular 8.5×11 ones are too tall, and set you apart from the group. I also use a laptop computer from time to time. A dice rolling program and adventure text on disk can cut down on table clutter.
Sometimes, a single die roll can heighten the tension and/or fun. If the players are goofing around, a die roll or two could help them to focus on the game. If they ask you what that roll was for, you can answer something like, “You’ll find out.”
Or, to make sure that a desired outcome occurs, the AM can roll dice, but not bother using the results. This can help a struggling Raid Team if the die is against them, or make things more difficult for a group of “Super Raiders.”