I had a pleco and a rainbow shark when i was a kid. I had one of those shipwrecked plastic boats in the bottom and they would fight over it, so i got a ceramic log for one of them to hide in, the shark took the log and the pleco the boat, they would constantly chase eachother away from their territories. It was fun too watch. Little did i know that neither of them should be in a 20 gallon tank let alone in one together. They died after about 2 years, i was a sad 10 year old. Good luck i hope they both live happy long lives and continue to give you joy. On a sidenote the oldest fish i ever kept was a bristle nose pleco. I had him for 10 years got him as a baby, he was my buddy.