Its always sad to lose a fish you've had for so long...condolences.
We had Oscars in a community tank, live plants, rockscape...never had major problems with them digging stuff. Mind you the tank was plenty big enough 90 gallons.
It was fun to go and net some fry in the bay, run up to the house and dump 'em in live!!! Scatteraction!
Oscars are very smart for fish...ours would come to the glass and beg when we got home and you could make them 'dance' wiggling your fingers back and forth. Really like oscars.
Now we have a 10,000 gallon tank, its 30' long, 8' deep and 7' wide, its full of Koi carp, pleco's, a fire eel thats getting near 8 years old, two Niger catfish and a red tail amazon catfish. The red tail must be getting on for 20lbs.
The tank is also our supplemental non potable water tank, we use it for the flush water, our hot water system and the laundry. It's filled off the roof of the house, and what comes out goes into the regular septic system. Oh yes, we have four big windows in the downstairs that let into the tank, it all backs into a hillside. Part of the reason for all this is our main source of water out here is what falls out of the sky, and we live on an island in a 120 yr old house that only had a little water tank of 5,000gallons, not really enough to see you through the summer, so my hubby got creative...
The filter pond is probably 500 gallons alone, multiple chambers, all biological. The last chamber gets vacuumed out maybe every two months, floating plants on the top as well.
My hubby has been a aquarist for many years, I think he's a bit nutty about it...but I have to admit he's inventive!