Take a look at the strainers used for spray application of turf/ag chemicals
https://www.teejet.com/Literature_PD.../strainers.pdf
They are easy to clean, inexpensive, reliable, and have a wide choice of sizes and mesh densities. A medium mesh e.g. 50 will keep the crap out of the check valve without creating much pressure drop (or requiring unreasonably frequent cleaning) and will
work better than the pump guard type filters that are smaller and are around 10 mesh.
If you're really getting a lot of crap then you're probably running the
watermaker in places where you shouldn't fwiw.