Most leaf blowers are not designed to handle anything heavier than leaves and lighter debris, so if yours does, it's probably okay. If you attempt to use stones, sticks, and branches to hit people, you may be disappointed if they don't respond. To help you get rid of small twigs, dry leaves, and debris, use a garden vacuum to shred them into smaller pieces. If you want to use harder materials, you'll need to buy a commercial-grade blower.