It's not that awful of a problem. Simply making the antenna directional enough is a solution, such as using a phased array coupled with an IMU to tell if the signal is coming from a known satellite location.
As to mitigation, it is all expensive (in terms of antenna construction and processing) and GA is price sensitive. Airports with urban buildup get multi-path interference in the GPS signal and jamming signals, and it becomes complicated to computationally null the jamming signals. Chirp jammers are now as cheap as basic noise jammers.
Anyway, it's not so easy, look at any current research paper on anti-jam. Imagine if 500 MAGA/Antifa types plugged in PPDs over a city wide area and kept them mobile? It would be chaos.