I find these 'tips' for using things with sharp edges like broken eggshells, sand, coarse grit etc to be absolutely bullsh**, no offence. Because when you think about it, the slime is an adaptation that allows slugs and snails to crawl over sharp things. It creates a layer to glide over and at the same time acts as a barrier to prevent wounding.
Besides, tests have shown that snails and slugs have no trouble crawling over razor blades. I'd go for some biological chemical like in pellets or garlic spray.
