Found a site with a lot of good info, if you want the link just let me know and ill provide it.
Basically it suggest that they are like fungus in that you can physically remove them thinking you got it all and they will grow back from the smallest left over fragment.
Chemicals don't work well, the only real solution is to introduce natural predators into the environment which I think is a lot cooler anyway....kinda like bounty hunters.
Anyway, the article suggests that Berghia verrucicornis or aptasia eating nudibranch is the most effective however there were some concerns as to the quantity of food as it only eats aptasia. The article also suggests using the copper banded butterfly the only concern there was that it also will eat small feather dusters from time to time.
Hope this helps, i researched this mainly because those things look nasty and I wanted to prevent getting them. The article also suggested that a nutrient rich environment was the main cause of the growth.....do you make your tank les nutrient rich then? Kind of a catch 22.