Dude,
I'd rearrange your rocks a bit. You need seperate piles. The dominant fish (or possibly pair) is going to try and consider that entire structure it's space.
Like was said before, they are VERY territorial, and quite honestly, they're bullies. I've seen a 1 inch convict cow an 8 inch oscar, several green terrors and a jack dempsey. They are just relentless.
That being said, I love my convicts, and to me they're worth MUCH more than $4.99.
That being said, I usually see the lil' fellas for for ~ $5.00.
Just make that one pile into several and you'll be set!