Ok.
You have legal options, other options, and illegal options.
- You can ask @Tim to prepare letters (Legal)
- If you know the person's parking habits, park a vehicle/trailer to block the car's exit. The land is your property and you can park where you like on your property
- Park another vehicle (old) right alongside so the driver's side so it cannot be used for ingress
- Put a large sign behind the car saying it is illegally parked, possibly with creative wording of your choice
- I mention various illegal options as a way of listing some actions that are not legal and should not be done:
a) accidentally drop an egg on the windscreen each day (clumsy people have been known to do that)
b) let air out of one tyre, with a note on the windscreen saying you've noticed a flat tyre. (dangerous having someone drive on a flat tyre)
c) borrow car dollies and move the car to a location on your property that makes it difficult, but not impossible, to leave
d) attach a chain to both driver's side doors (carefully and without damaging the car) so driver's door cannot open
e)
[insert prank of your choice]
As a lawyer I am obliged to recommend option 1.