You say this is *your* car park, but you need to be clear what this
means before you take action. Either it is reserved in some way for
your use (either because it is privately owned or because the local
authority has set it aside for your exclusive use) OR it is a public
parking place. If the former, you have my sympathy, and perhaps some of
the actions mentioned in this thread will help. However, you should
really turn to legal remedies rather than vigilantism - you're more
than likely to get confrontations with the kind of people who invade
other people's parking spaces - good luck, take a big dog with you.

If you don't have legal right to exclusive parking, on the other hand,
tough. Suck it down. There's nothing more annoying than those nutters
who leave their own personal traffic cones on the street in front of
their house. If I parked in a legal parking spot and someone vandalized
my car, I'd take photos, have it professionally cleaned and take them
to the small claims courts for costs.

So which are you, aggrieved victim or cone-nutter?