I like the floating plant idea. I always assume people don't want floating plants in aquariums. I seriously doubt the other oscar is going to act as a dither. My guess is they either spawn and destroy the tank by moving their bed around. Or they try to define territories and they rearrange the tank int he process.
As for dithers, BA tetras are awesome. They are sturdy and fast enough to keep up with pretty tough tankmates. Once they get to the three inch mark they are nearly indestructible. Giants are another great choice. Once they hit the 2.5 inch mark they are way too fast to be eaten. I used to keep gambusia with my oscar. When I put them in one by one he would eat them. I was in a hurry one day and dropped 20 in there and they stayed for months until I went on vacation and didn't feed. I rarely saw fry so I assume they got eaten. I have no idea if other livebearers would work or not. I knew I shouldn't have entered this conversation now I miss my oscar and want another one.
As for dithers, BA tetras are awesome. They are sturdy and fast enough to keep up with pretty tough tankmates. Once they get to the three inch mark they are nearly indestructible. Giants are another great choice. Once they hit the 2.5 inch mark they are way too fast to be eaten. I used to keep gambusia with my oscar. When I put them in one by one he would eat them. I was in a hurry one day and dropped 20 in there and they stayed for months until I went on vacation and didn't feed. I rarely saw fry so I assume they got eaten. I have no idea if other livebearers would work or not. I knew I shouldn't have entered this conversation now I miss my oscar and want another one.