Depends on the situation - if its on the ground, and you've got slate chippings one side and gravel the other, and the area's big enough, Victorian rope tiles or a modern equivalent?

A lot depends on whether you need to walk over the dividing line - you don't want to install a trip hazard. Why not have a good look at some big garden suppliers' websites to see what's available & check out the DIY stores' websites too.

I separated one edge of my rockery and the lawn with a piece of 4x4 timber at ground level and it has worked well, as the lawn mower goes over it and the stones stay on the other side

Hi bamboo/beattie

thanks for your help,the Victorian tiles sound nice we do have slate one side and shingle the other so I guess we need to visit a garden center or DIY store... Thank you both.

Check out Bradstone's (aggregates company) website first - they have a range of those available, along with brick edgings, kerb stones, etc. Their products are stocked by various large garden centres, Selco and some at Wickes. The other well known company is Marshalls, they're on line to look at too, but they don't seem to have so many options for this kind of thing. I only know because I've spent the last 4 days going through their brochures to select paving, edging, bricks and gravel for a design.

Thanks bamboo,will do!

thanks drc726,
everyone`s comments are certainly giving me something to think about ,thanks guy`s .