Oh regarding zooanthids. They take okay to superglue but anytime you can scrap or chisel two connected polyps off at once, the elastic can go between them to hold them to a rock.
All elastics are not created equal. The tan kind the LFS use are best. There are several sizes. Others seem to have some chemical irritant.
A piece of Saran type plastic food wrap is totally non irritating to coral. Use that between the elastic and the coral if irritation is a problem.