Hi Bobbthebuilder, One interesting way that we have seen recently is to use resin bonded stone, as in the type that is used to create resin driveways. Some companies even make pots and planters with the resin bonded stone.
I'm sure that there are lots of other ways to make your own too but if you don't want to, you can buy artificial rocks for aquariums that might work - I think you can even get them on Amazon!
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!