There is a simple way to prevent the pain of mine-and-dump.
All you need to do is limit the difficulty adjustment to (say) 5 or 10 percent. Here's how it works....
One day, your difficulty drops low enough that you are suddenly "the most profitable coin to mine" and a skillion GH/s jump on board. They mine the hell out of your coin until the next difficulty adjustment (targeted for 24 hours, but they're likely to solve that many blocks in 1 or 2 hours if they so far outclass the regular miners). The diff adjustment happens, and your difficulty goes up -- but it goes up just 5 or 10 percent. You are probably no longer the "most profitable coin to mine" so the mine-n-dump miners all jump on a different coin, leaving you with approximately the hash power you had before, and 5 or 10 percent higher difficulty. So now, instead of your two-minute average block times you're looking at two-minute-and-six-second block times (5% adjustment) or two-minute-and-twelve-second block times (10% adjustment). And while the rapid mining hour or two may be pretty silly, the longer-term effects are minimally disruptive.
Remember, all the mine-n-dumpers just want to jump on the "most profitable coin" immediately, and jump off it again immediately when some other coin takes that slot. Getting 5% or 10% harder to mine will usually take you out of the target slot just as effectively as getting 1000% harder to mine, and if the higher hash rate is not sustained, will do so far less disruptively to regular users. If one adjustment doesn't get rid of them, two almost certainly will -- especially because the coins these clowns aren't mining will be lowering difficulty in the intervening time.
+1 to this for me too.
I think a hard fork introducing such a huge change as stated (retarget time from 24 hours to just 1 hour) wouldn't be good.
This would change the entire coin too much, and thus it would basically be like changing the coin itself.
But set a limit to the % of the diff retarget could be a valid solution.
