Yeah....the baited wineglass trick won't do a thing for a mantis. They can swim amazingly fast if they want to.
El Diablo.....don't take this as Gospel....it's just a generalization. Pistols USUALLY only click at night and USUALLY only once in a while. However, have a Electric Blue Halloween crab come near the den and you will find that they are quite capable of multiple clicks if need be.
Mantis sometimes will only click once but sometimes they are extending their den in the LR
and will click repeatedly or if they grabbed a snail, they will bang on the shell until it is either cracked open or the snail is stunned enough to be flipped over. A snail shell graveyard in one area of the tank would be an indication of a mantis and also where the mantis den is.
You should also look for empty snail shells or small live rock rubble that change position. Just keep a mental note of where the small pieces are and keep watching to see if they get moved. (You haven't seen anything until you see a mantis swimming with a piece of rubble that is bigger than the mantis). More than likely, they are being moved to the opening of their den.