Dealing with neighbors that want to park in my yard

Had it out with my neighbors a couple weeks ago about them feeling entitled to use my yard as their parking lot.  You can see that they’re like 3 feet into my yard AND parked right next to the 24 hour towing sign:

My solution:

I’ve had to do a bit of research on what kind of grass will grow there and I settled on “Mondo” grass, which it turns out isn’t even a type of grass at all, but more related to lily and will spread to fill that entire section within the next 2-3 years, then will spread to the rest of the yard if I don’t put in a border or lawn frame to keep it at bay.  Pretty easy and I have plenty of time to figure it out, at least if the damn neighbors over there keep off the grass.