I would like to make two points here:

First, as previously mentioned, You should have an area that is OFF LIMITS to anyone who is not currently flying/instructing. Let spectators know to stay out of the area (usually behind a safety fence) And if someone does come out there, give them a good strong "Get out of here!". You may hurt their feelings, but you can apologize after you have safely landed.

Second, For all of you newbies who can't wait to get rid of their rubber bands, take a look at the minimal damage that occurred in this crash. If that wing had been bolted on, there would have been SUBSTANTIALLY more.