Spectators? Statistically, this is not a tournament golf problem at almost any level. Nor is it an equipment issue, as if the long hitters are statistically the wild ones. This is every day golf, on older, (generally) tighter spaced courses where C and D players (mostly) who hit it 170-225 (mostly) hit a wild shot that finds the next fw, or beyond, LOL.
I was surprised to learn recently, reviewing some of the ball flight studies by Gene Parent, where he ran a ball test at 95 mph (amateur player) and 110 mph (PGA Speed) with a driver. They both averaged 60 mph of descent ball velocity. i.e., getting hit by C/D golfers hurts just as much as getting hit by Tiger Woods. The combination of atmosphere, ball weight and gravity cause all aerial shots (a stinger would be much different) to descend at similar rates as they run out of energy. A Tiger shot has more energy when it leaves the club, but falls when it runs out of forward energy, i.e. gravity takes over.
The best ways to provide safety start with adequate fw spacing and no cluster areas in oft found areas from other holes, then vertical barriers (ugly nets better, but most opt for trees) in higher risk areas. Yelling fore is a last resort mitigation option because few golf courses have enough acreage (i.e. Sand Hills) to provide the first option - more than adequate hole spacing.