but if it has holes wont they be able to see each other and wear themselves out?
Yeah, the fish will be able to see each other through the mesh and get stressed out. However, if you use TWO layers of mesh about a half inch apart, they won't really be able to see each other.
Here's what I did with mine... sorry about the dark water.. it's from the Indian Almond Leaves:
^ So I used two dividers made of black mesh and report cover sliding bars, and I sandwiched some java moss between the two layers. But even without the java moss, the guys couldn't see each other through the two dividers set about an inch apart.