Rushock Bog in Shire. Go during evening. The key is to kill all gnats, and frogs, these I believe help spawn the slugs. I went once before and they were real scarce even with tracking. I started killing gnats and frogs this time and some areas would have 3-5 in them when I looked around. Took less than 1 hour to kill all 90, 30 for deed and 60 for advanced deed.