Could you post a pic maybe? Not sure what rubber thing your referring to unless you mean the suction cups which are known for becoming loose and then falling off. I'm guessing you have a submersible heater so you could leave it in the bottom.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.