Ferret problems, please help?

I have two male ferrets Jack 4 and Cooper 3. I have a problem with them both pooping all over the entire bottom of the cage, there are litter boxes in two corners, and food bowls in the other corners. They go in the littler pans in their foot bowls, in the center, they go every where doesn't matter. I have no idea what to do. My second problem is Jack Bites the back of Coopers neck, he just latches on and stays there. he did this when i first got cooper, dominance I under stand, it wasn't to bad i would have to get after Jack occasionally pull him off tell him no. He started to do it less and less it eventually got to where he did it very seldom, now hes back at it and it seems like he on him every waking minute, its to the point where it takes every ones help to keep an eye on them. I have put stuff that takes bad on coopers neck, didn't help, now we just pinch jacks ear or scruff to get him off, them tell him no and put Cooper somewhere else in the cage. please any tips im desperate.