Shaw, up to recently there has been 2 main types of snail/slug bait on the market: metalfahyde and iron phosphate. Metaldahyde has been around forever and is the active poison in regular snail bait. It works quickly (you may find dead snails and slugs the next day after application) but it has been linked to accidental poisoning of pets and other animals. It is not labeled for use around food crops and breaks down quickly in wet conditions.
Iron phosphate, on the other hand, is sold as being non-toxic to animals. Slugs/snails will stop feeding after ingesting this type of bait (Sluggo is a major brand) but it can take up to a week for the snail and slugs to actually die. Any excess bait not eaten fertilizes the soil. It is typically preferred over metaldahyde in humid and rainy conditions, too. I am hesitant to say that it is absolutely safe, though,as there appears to be a handful of reports suggesting otherwise but it is labeled as the "safer" alternative. Unlike metaldahyde, it can be used in the vege garden, also. This is the type of snail/slug bait that I use (Sluggo brand).
There is a newer bait on the market, sodium ferric EDTA, which is suppose to be similar to Sluggo but which actually kills the snail/slugs within 3 days. I cannot comment on this one as it is new to my area and I have not tried it.
I hope this info helps.
