California is in the middle of one of the worst droughts on record. The state recently manadated that cities reduce water used by 30%, including limiting lawn watering to twice per week. Very expensive lawns in uppity places like Palo Alto and Beverly Hills are going to die.
Enter the retractable trampoline--or rather, retractable shade.
Place a few anchor posts in your lawn. Hang a roll-up shade between the knee-high posts and stretch it over the lawn to anchor posts on the opposite side.
The shade is coarse weave, like the trampoline, to reduce wind force. And it's green-colored to hide your ugly lawn underneath. When guests come, simply unhook the shade and it retracts to reveal your gorgeous vibrant drought-saving lawn.
Come on entrepreneurs, the market is hot. Get this thing in stores by August!
Gotchas: Wind and tension. A trampoline has hundreds of pounds of tension supported by a big aluminum frame. You can't afford that. Also, the longer the shade, the deeper that dip in the middle. There may be some magic to the trampoline that it was high enough to block the sun, but not low enough to trap heat.
Bonus: You probably don't need a shade for your entire lawn, just cover places that get a lot of direct sun in the afternoon. And the shades don't need to completely cover the lawn. The sun moves, so gaps in the shade equal to about the height of the shades off the lawn will "wash out" as the solar angle changes.
Double bonus: figure out how to get solar power from this.