use the hook over kind. they make them in plastic and metal.. i use the cheap suction cup kind like you guys are having problems with. they are like 1.97 at wallmart. buy 2! remove the green suction cup and ring from 1 and add it on the other thermometer. now you have double the suction wich really helps. also, make sure you not only use your mag scrubbie to clean the mounting spot, use a washcloth and make sure there is and imaculate clean surface. hope this helps. stopped my broken thermometer problem too. my fish cant bang the glass tubes onto the glass anymore!