Slugs

Hi. I grow lettuce in a raised bed. The bed is covered with insect net, copper strips around the side and a covering of grit and 'woollen anti slug" pellets. Guess what...yes slugs. I do not see any climbing into the bed so I'm convinced there are eggs hatching within the bed. Any ideas how to 'clean' the bed soil? I don't want to use slug pellets as I have a dog and I don't want to use them anyway. Appreciate any ideas. Thankyou