I've just read the most fantastic article on stones by Anthony Doerr - it was published in Orion magazine and can be read online. It's really worth checking out as it says so much about the relationship between people and stones and how they are going to be around for so much longer than us.
Meanwhile, I'm still pondering the next stone but I'm glad to report that I'm going to see Alec Peever, the stone carver, in April and we're going to discuss the shape and substance and design of migrating stone number four. It's curious with this one - i have a clear idea of what I want it to look like, but as yet do not have a clear idea of where it needs to go.
So, for now all I can do is stay open and trust that the answer to this dilemma will arrive in its own good time.