the pellets work, but I've never gotten them all with pellets. Slugs are my main issue, sometimes those stupid bush snails (what you probably had). There are always a few in there, go for months without seeing any and then you find one in the wrong spot.
If I get plants from a known sluggy source (I have a few), I soak them in a large bin of water over night. The slugs (and snails) seek air at the surface, and they are easy to spot. I put a good slug of dish soap in the soaking water. Repotting them afterwards never hurts, paying particular attention to the roots. Slug and snail eggs are relatively large, and spherical (up to the size of small pin-head). If you see any, get rid of them.