I have a similar concern at my property, but fortunately I have ample parking space near my premises for 6–8 large vehicles. What has worked well for me is making it very clear before the guest arrives that all vehicles must be parked Properly in front of my homes.
I also have a simple parking sign at the entrance showing guests where to park.
In my experience, prevention and clear instructions before arrival are much easier than trying to correct the problem after guests have already parked outside.
If you have sufficient space, I would make private on-site parking a positive feature of your listing rather than treating it only as a restriction.