Slugs are found in areas close to the ground that are wetter, shadier spots. If the area has these conditions, it will be harder to stop them from coming back. Non-chemical options include pruning plants to open up the canopy and allow more air flow, watering earlier in the day, and avoiding overhead watering.

Sprinkling Diatomaceous earth around plants can help kill slugs but won't deter them. Iron phosphate and Ferric sodium EDTA are two chemicals that will kill slugs when ingested. If using pesticides, be sure to read the label before use. 

Ferric sodium EDTA