Some thoughts about it...
My brother and I think about making a line for summer holidays, but we have no experience... We thought about several floating devices and think that those inflatable sailing race buoys would do very well. They come up in several sizes, are easily visible for others on the lake/sea and -well- thei`re inflatable. Thing is that they cost quite a bunch so if you`re on a tight budget like we do, this may be no option. For anybody else, they might be the perfect choice. Don`t forget to attach something the divers can get a save hold on the surface, kind of an ring or so (check out the cyprus photos...)
The rope is easy, go to the sailing shop and buy some thin white rope(thick enough to have a good grip, thin enough not to be dragged around too much by the current, say 10mm or so). We also think about using some weight disks as used for barbells. Make sure you take enough weight to make the thing stable.
Do we still need an anchor? Don`t know actually, I suppose if you take enough weight at the rope`s end this shouldn`t be necessary... And, BTW, you don`t want to go down to tear a stuck anchor out of the mud or rocks by the end of the day I think!
As I have never done such a diving line before, this is all just thoughts... If there`s anyone who REALLY KNOWS how this is to be done, please correct me if I`m telling wrong things. You might save my holidays.
Greets to all, dive often, Joe
P.S.: Make sure the whole thing is stable enough to savely carry at least two divers ascending at the same time (see 20 freediving rules).