#1 - Super glue gel

#2 - They are fairly difficult long term. 1st you have to feed them as they are non photosynthetic. Cyclopeeze, daphnia, baby brine will work well. 2nd they easily get overgrown by algae, especially cyanobacteria, as they o not excrete a mucus like most corals. So you need to keep water quality high to prevent algae problems. If you do see some algae starting to grow on them the easiest thing to do is just rub it off with your fingers.