if it seems sturdy enough it should be alright but you can always secure rocks with aquarium putty, zip ties, or prior getting it wet use concrete, and/or even drill holes and use pieces of a plastic hanger and im sure there are other methods.
any type of zoo or paly will release a toxin stressing any near by corals ( also depending how large your tank is/how much was released ) and may then cause that coral to release toxins of its own, deplete the oxygen available for fish respiration, stings your eyes and open cuts and is best avoided when possible. fragging these corals is another cause to release the toxin and sometimes even squirt ( which can shoot right into your eye, so safely googles are suggested )
you have to make these guys mad for a release but i know personally i wouldnt take it lightly. i lost an entire mixed reef in 1 day. i had woke up to a tank as milky as milk ( no joke ) and corals and even fish gone. my skimmer wasnt working at the time so that only sped up the process. the tank was mostly LPS, zoos and softies but all SPS was bleached white. I can only assume that my huge colony of green palys was set off ( it had to of been easily 1,000+ polyps. ) and it started killing other corals which then died fouling the water more killing other corals and so forth. fish suffocated and were lying dead on the bottom of the tank. now if you have a few mini colonies of zoos in a tank i wouldnt be getting paranoid. this is just something to keep in mind. in other words, only put your hands in the tank when you absolutely need to.