Leaf vacuums have the suction power to pick up leaves. Most rocks are too heavy. However, gravel is the exception. Picking up a few pieces of gravel isn’t a problem unless the vacuum has an impeller to mulch leaves. While a pebble or two won’t ruin the impeller, avoid rocks and other hard debris when mulching. And, if you are near gravel, it might be best to turn the impeller off until you’re clear of anything that could be potentially harmful.