Few Monti Question

I have about a 5" piece of monti cap in my tank.

1. Do i have to glue it down or will it attach itself to the rock by itself?
2. Sometimes snails or crabs will walk across it. Is that normal? There is no algae growth on it.

 

I would glue it to the rock, so it doesn't move. It would eventually attached itself, but SPS is extremely easy to glue, so you might as well, rather than taking the risk of it falling.

Also, crabs/ snails will climb on them, but it doesn't do any damage. You will probably see the little polyps close up, but they will open again after a few seconds/minutes

 

I've had mine for 6 months (now 6" x 3") and didn't glue it down. It never fully encrusted to the rock, crabs climbed on it, and it fell twice. I has good coloration and grew well otherwise but I suggest gluing to the rock to prevent this (and landing face down on sand can irritate it and cause tissue loss) and I assume it might also help in the coral encrusting itself as well.

I will be gluing it to the rock in my new tank when I move soon.