How to defend against drones?

Drones are a new, very cheap reconnaissance and offensive weapon that is difficult to defend against. Most often, they are so small that radars cannot notice them, and even people from the ground cannot see them if they fly at heights greater than a kilometer. At night they can fly at much lower altitudes without the risk of being seen, and then they can only be heard.
We can defend ourselves against drones in a passive and active way.
Passive defense is very simple. It is enough to hide people and the army under canopies, or in underground shelters so that drones cannot spot them. But drones also attack infrastructure that cannot be masked. They also attack moving columns that cannot be hidden.
Therefore, active defense against drones is necessary. We can shoot down larger drones with anti-aircraft missiles, which are many times more expensive than the drones themselves. They can also be shot down with anti-aircraft guns and machine guns, if we see them. And when they fly at a height of several kilometers, then we can hardly notice them, especially at night.
The solution to this problem is to arm your own drones, or small single-seater slow planes with propellers, with automatic shotguns. Fast jets cannot fight drones because the time between the pilot seeing the drone and flying past it is too short to react. Unlike them, slow simple and cheap agricultural planes can be armed and used as drone fighters. Such very cheap planes armed with automatic shotguns could slowly circle above the area they are protecting at a height of several kilometers, and when they see a drone they could approach it from above within a hundred meters, and destroy it by automatic fire with ammunition that is usually used in hunting rabbits, geese, or ducks.
In order for such a plane to be able to notice a small enemy drone, it should be equipped with high-resolution panoramic IR cameras with a ten-fold magnification of the image that records both day and night. In addition to cameras, planes could also be equipped with sonars that would detect all objects at a distance of hundreds of meters. Directional microphones could also be added to detect drones by sound. All these sensor tools should be controlled by a small computer that would turn off the sound of the plane it is on, and it would have to have an application that would direct the weapons depending on the direction and speed of the plane they are on, and depending on the speed and direction of the drone's flight should be shot down. When the enemy drone is detected, the plane should approach it within a hundred meters, and shoot it down with automatic shotgun fire.
In the same way, they could arm their own medium-sized defense drones that would fly over the objects they protect, and which would be controlled by soldiers from the ground, based on what they see themselves and on the basis of the information they get from the cameras and sensors located on the very defense drone. Such defense drones specialized in shooting down other drones do not exist on the world market for now, and even small countries could produce them with existing technologies.