Although no one at our grass field is flying anything with more power than a 300 4 stroke, at the present time, what works well for us is a pair of approx. 1/2" dia. metal stakes (rebar could work well here ) driven into the ground about 3 ft. apart each covered with a "swimming noodle" (kids pool toy ). They stick out of the ground at 18" plus and restrain the wings. We have had no accidents due to lack of restraint and liked the effectiveness so well that we drove holes into the turf and planted 8" pieces of PVC tubing into the upper part of the holes to preserve them. After the first hole "drilling" session no sledge hammers are needed to drop our stakes into the holes at each flying session. If you intend to run the engine up to full power, first apply full up to the elevator to keep the tail on the ground.