The pellets are supposed to be rain resistant and effective for 10 days ....I'll only put the salt - large pieces of the cheapest sea salt, along the bottom crevice outside the breeze block edge - yes, it'll also get washed away, and as it's only on paving stones, it shouldn't affect the soil.
I watched an experiment where crushed eggshells were used - despite washing the shells to remove the gooey stuff, the slugs actually preferred to go through them to get to the lettuce leaf, than the one without protection! The area is already surrounded by sand (and remnants of grit), so hopefully that helps a bit.
I'll be planting chives around the perimeter of the main potager - supposed to also deter our slimy friends, and we like chives, so double bonus!!
Got another lot of seedlings on the go now, and hopefully I will have perfected the system before they're big enough to plant out! I will not be beaten!
Unless of course the slimy brigade find a way to parachute down! The foil-protected sections are definitely working ......