slugs and snails

Hi can anybody tell how to stop slugs and snails eating my clematis every year it is the same.I've tried pellets around the bottom, copper tape around the pot and keeping foliage from other plants away so that the slugs and snails can't reach across.Its getting very disheartening now ..help .. 

I'd suggest that you go out after dark with a torch and pick them off. This might show you where they're coming from but, in any case, will decrease their numbers significantly if done every night for a few weeks. It may well be that they are living in the clematis itself.

Definitely take a torch out on a warm damp night.  As Alina says, some snails actually live within the leaves and don't often go down to ground level.  I have hundreds of them living in the ivy covering some of my fences - common yellow and black striped ones.