we tried something different last year and are doing again this year we like lolla rossa lettuce but so do the slugs I cut the bottom out of plastic pots about 6-8 inch dia. then with a brush go around pot just below ridge on pot with vegetable oil then dust with salt this gives a band of salt around pot the slugs and snails wont go past this with carefull watering this lasts some while and helps keep lettuce or rocket clean. nothing worse than slime on what you will eat. good luck. sorry meant to say stand pots on veg bed fill with compost.