Underground pests...... Spray some foam insect killer around the hole at night, to prevent the sentinel hornet from waking up the herd. Then pour a little gas down the hole, cover the hole with a rock. The gas fumes will kill them, the foam will kill the ones that almost escape.
Aim a flashlight in the general area of the hornet nest, leave the flashlight there. Come in from the other side. itll distract the sentinel hornet. Suckers love my wife's pool.