If you're in a biome with a moderately abundance of wood, go with weapon traps instead using simple menacing spikes, giant corkscrews and spiked balls. (I prefer the latter if it's a trap that will be placed on a raise section of walkway with the goal of knocking the enemy off into a pit to the side.)
The big downside of stonefall traps is that they're one-shot deals. They toss the stone at whatever is in that tile, then a mechanic has to reset them. At least with a weapon trap, it runs until it jams. And the ones that use blunt weapons don't jam that often (but they're not as deadly as edged/piercing, but still far better then stonefall).
Wood-based weapon traps will kill all nuisance critters like the monkeys/wolves, and do a fair bit of damage against the elves too. But you'll want some copper/silver weapon traps using edged/piercing to tackle more heavily armored opponents. Mostly, they're useful for getting the enemy to dodge off the path, down into a pit, which makes them path around a few dozen tiles before they can get back to where they fell off.
OTOH, even an armored opponent will have a tough time making it past a line of 8 wooden weapon traps (especially if you use masterwork mechanisms and weapons) without taking at least *some* damage.