I have been involved with an outdoor quilt show for years. We are all quilters. It is put on by the local chamber of commerce to attract people to town. We have a group of dedicated volunteers, whie glove ladies on patrol constantly. We have a secure hanging system with wooden posts holding up rope, everything staked down with tent stakes. Quilts must have a hanging sleeve and we thread the rope thru the hanging sleeve. It is in a town square setting. We have a set of SUVs strategically placed around the square in case of bad weather. We have a group of on call folks, that, if the weather turns bad or the wind kicks up, race into town and get everything down and thrown into the SUVs. Every quilt must have a sewn on label and they are placed into pillowcases with the entrants name and number and every quilt has an entry number assigned to it and pinned onto it. Entrants turn in their quilts a few days before the show. No owner pick up on show day. All the quilts are put back into their pillowcases, checked back in at the central location, we make sure we account for all of them. Owners pick them up the next day--no exceptions.
My only advice is to enter a show that has been around for awhile and has a good system worked out. If in doubt, call the folks putting on the show to see how it runs. Don't enter anything irreplaceable. Bird poop is always a risk. If your quilt is not washable, don't enter it if you don't want the risk. We try to have the ropes suspended about 10 feet above e ground. It would be difficult for someone to cut a rope, get a quilt down and run away without someone noticing--but it could happen.
It is magnificent to see our town square filled with quilts swaying in the breeze every summer. I am there at sunrise hanging ropes and quilts, work 1 or more volunteer shifts, go home for awhile and keep an eye on the weather, then go back and work the take-down shift at the end of the day.