Stealth Heaters - A+

[fkshiu]

Stealths ARE Visitherms (pretty much)! They're made by the same company.

There's no such thing as a bulletproof heater on its own. Ebos used to be as close as you could get but they've gone downhill since Eheim bought them out.

The only way to be 100% sure is with an outside controller. Short of that you can use multiple small heaters rather than one big one so if and when one sticks on, you'll have time to notice before it fries the whole tank.