[Coral-List] in situ measurements

[Kaylee Smit]

Hi there, my name is Kaylee Smit and I am honours student at the university of KwaZulu-Natal, Durban, South Africa.
 
I am wanting to measure coral growth in situ on an artificial reef. Because I am new to this list, I could have missed this discussion topic, but I am wanting to know what putty's or other substances or materials have been used to mark points underwater on the reef, or to secure 30x30cm quadrats.
 
Thanks 
Kaylee Smit