The best technique is a network of nuclear powered mass-drivers, as many as needed per errant asteroid.
They would land on, and then redirect, using the body's own material, into a safer or more useful orbit.
Certain rules might need to be established in order to prevent hazardous small rocks from flitting about the system. The size of the propellant mass-load, the direction of the expelled mass, and so forth.
Such devices could be used to harvest asteroids from any orbit, from the asteroid belt, the Trojans, Earth grazers and even the Oort Cloud. The longer it has to act, the less drastic action is required.
Please note, this could be a requirement made on privately funded business ventures. They would be unlikely to object too much, because they could bill for services, and reap the harvest of material.