FWIW, as a 2019 parking crew volunteer, I would recommend maybe putting up a "fence" along the far side where the house is the day before the event?  I was parking people up to the "long grass" edge and someone from the house was yelling at me to make sure when people leave, they don't drive over their lawn.  Fair direction.  I did ask people to not drive forward when leaving but of course I have no idea if they did.  Anyway my thought was to "steal" some CX poles and tape just to place along that edge for 2020.  Would take maybe 10 minutes and at least help reduce any future incidents.  That and I expect the cost would be zero.

Thanks for listening!

-Terry

Re: temporary barrier for parking.  I have a bunch of stakes, 4 to 6 feet long, and we have Caution tape. I used them at Gathland one year, roping off an area to discourage riders from walking over to the tree line to urinate.  We can use them at Thurmont.