Need a thug-proof way to keep trespassers from parking in my yard. Any suggestions?

My driveway is in the back alleyway. Our yard is slim and half of it is driveway so we use the yard as an angled parking lot. The problem is that people keep parking in our yard, and usually we don't park at the bottom but sometimes we need the room. Whatever we put there needs to be movable so we can park other cars when people come over.

It's several different people parking there. I live in a hood (not a neighborhood because these people cant be considered neighbors) so:

I can't have them towed or ticketed or my tires get slashed.

Reflective driveway markers get stolen.

Wooden fences in the area get tagged by kids and are expensive.

Concrete blocks end up either stolen or in our windshields.

Boulders aren't movable for when guests come over.

Chain link fencing attract kids, which leads to playing on our vehicles, scratching them.

Can't put up a sign that says "do not park here yada yada" because it just gets tagged by kids.

My only other thoughts are to use a railroad tie, which blocks about 2 parking spaces, and can be moved. Or fake bushes with a concrete block inside to keep from blowing away. Do you guys have any other suggestions?? It really sucks living in this hood so taking it to the internet means I've exhausted my ideas. I really appreciate any ideas.