Well, the part that sticks out is a snail or current knocking off the shroom. Unless you have a PH pointed directly at it, there is some other reason why it jumped off.... which could be good or bad. If your shrooms don't like their location, they will unattach themselves and float around your tank until they find a good spot. But on the other hand, if your shroom are happy, they can reproduce by moving to another area and split or drop baby shroom off, depending on the type of shroom you have. My ricordia will grow another mouth and split down the middle. I have some purple ones that grow a baby on its side and then it splits off when its ready. My giant green hairy and my red shrooms usually just show up next to a larger shroom.
Anyways... the method Rick suggested is probably the sure-fire way. Using netting or tule(wedding veil), I've found that the shrooms seem to get irritated from something touching them and take longer to attach, sometimes. Goodluck and sorry for the rambling!
-Big Dave
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There's nothing like feeding your starfish for your party guests!!
120 Reef
SDSBBNR (sorta deep sand bed but not really)