How to mark corals using DIY U/W buoys

[pilz]

Dear all,

I'm doing a research on coral reefs. Now I have about 4-5 locations, with in total about 25 transects to survey. These transects will be fixed during my research. I'd like to mark the starting points of my transects with something like a small U/W buoy. However as there are many other (recreational) divers in my area, I can't use any surface markers or fancy things as this will attract other divers and they might remove my marker.
So a couple of questions here:

- Is there anybody with experience with this?
- Will it be a good idea to use for example small (500 mL) plastic bottles, attached to a 2-3 m line (in ~10m deep water)?
- How to attach such a line to the (coral) substrate, without using any concrete structures?

Your help is much appreciated!

[smellzlikefish]

I come across transect markers occasionally here that consist of a rod that has been pounded into the reef.

When attaching transect lines to the substrate, we would find a piece of dead coral nearby to lightly tie the transect end to. You can also find a rock to anchor the transect if it starts in sand. Be sure to anchor both ends in some way.

[ScubaBB]

If there are empty spots on the bottom, you could use a stone at the end of your 2-3m line.