For the past five years, it feels like I’ve written the exact same sentence about the outdoor Heaven & Earth shows organized by the Center on Contemporary Art: Get there early before the art is vandalized or stolen. So it goes this year again. A city anti-graffiti crew removed some of the faces painted on trees—using natural pigments—by Richard Metz. Of the installations by 14 artists arranged along the ravine park’s walking trails (about three miles), most remain intact.

For now. This year’s theme is “Acclimatized,” meaning the works are meant to withstand what CoCA calls “the intensity of scrutiny.” (Funny, but I never destroyed anything by looking at it.) Last year there was arson and theft, and the city’s overzealous cleaning crews have also previously carted away sculptures, mistaking them for junk. But then, humble materials are appropriate to a temporary outdoor show, and most of the pieces here are made of modest wood scraps, small stones, yellow police “Do Not Cross” tape, and even plastic yard signs (Elizabeth Gahan’s hive-like Tree Pods, some of which have been stolen).

I think that CoCA and the artists have pretty much accepted the peril—now part of the drama of the exhibition, which opened last month. A subsequent CoCA press release advised visitors to go “before it’s TOO LATE.” Alan Fulle’s kid-enticing Spiritual Play Tower (basically a wooden fort) has meanwhile been deemed too dangerous to enter. Again, more drama. I think size is the best guarantee of security: Make something large or substantial enough that it can’t be carted away or torched in the night. For now, for that reason, in the field next to the visitors’ center, Suzanne Tidwell’s Half Court of Croquet . . . Anyone? has been unmolested. Kids can push inflatable beach balls through the colorful hoops (planted securely in the turf), and who really wants to steal a 10-foot croquet mallet? What would you use it for at home? Carkeek Park, 950 N.W. Carkeek Park Rd., heavenandearthexhibition.org. Free. 6 a.m.–10 p.m. daily. Ends Oct. 20.