My fahaka did the same thing a while ago, looked into the tank and noticed the thermometer was broken, luckily he didn't injest anything i'm aware of and all the nasty parts of the thermometer were intact so i removed the broken glass and what lead weights I could find. since then I haven't used a thermometer in the tank, rather I monitor my temps from time to time with a traveling thermometer that I use in several tanks.
I've been very concerned about teh heater ever since, both the cord and the heater itself. I have a ebojager 300 watt heater, so it's pretty thick as far as the glass goes, but when I feed something like freeze dried krill, it always seems to drift over near the power cord. to resolve that, i lowered the water level to below the cord so that nothing but the glass part of the heater is exposed. it's also placed in a corner behind the intake so it's a tad bit out of the way (still accessable if he wanted to get to it)
Sump would be the best option, and the one that I'm looking into. also would be a nice place to breed snails and other plants.
for the record, I have a plexi tank for my fahaka bacause of the tank buster aspect.
