you'll never find one in your tank only one has been found in a saltwater tank so far and that was in the UK (the one in the pic I posted actually) but they are the things of nightmares...
I find myself more concerned with bacteria in the tank so I wear Nitrile gloves & a rubber band around the wrist whenever I mess around with the tank or need to grab sharp rocks. Of course it helps with my psycho clown who hates my guts & dreams of murdering my hand.