As soon as the shells get wet the snails can just glide over them.

I guess you could break the shells up so there were lots of sharp pieces and that might work.

@Moon_growe - Slugs and Snails produce mucus and they can crawl over razor blades with no injury, so a sharp shell is not deterrent (have found them hiding in shells :( ). Perhaps the salt in shells would deter them or if you effectively ground the shells into sand sized pieces but that would be more trouble than it is worth.

Amazingly when we laid the paving slabs on the patio we noticed a lot of dead a dying slugs and snails on them. We could only assume there was something in the coating that totally disagreed with them. As the coating is slowly wearing away there seem to be less each year.

Hi, welcome to GoY, I find that these so called slug deterrents, are no use whatsoever, the only things that work are, dropping them in boiling water, salt sprinkled on them, or slug pellets, may not be p c, but neither are the slugs, Derek.