Currently I'm using yoghurt-mixed-with-dog-kibble & then sealing it with a lump of cream cheese. I may try peanut butter when we're out of that. The trouble is she's just *really good* at getting things out of other things! When the weather warms a bit I'll be able to freeze stuff, which would be better. The other irritant is that we don't have a microwave so I can't do melted cheese, which would otherwise be a v v good solution. I'll check the link out, thanks!