Wait, I see under your avatar that you have a bun that says *no name yet*...does that mean you recently got a new bun?
Did these problems start about the time the new bun came home, or have they been before that?
I'll tell you...I still have some buns that aren't yet altered...and we're trying to get a house...so just in case (it's a rental) it has carpet, here's what I have planned to do. (Please note that I have not actually tried this yet, but I've talked it over with my husband, who is really good at planning this sort of thing, so I think it'll work.)
Now, the cages already have pegboard as flooring inside the cage...but pegboard has holes in it (obviously, lol). So, we're thinking (because we do have three unaltered does and one unaltered buck...kept VERY far from each other, don't worry) that we'll buy big sheets of linoleum and put that underneath the cages just in case someone has an "accident" and goes outside the litterbox. Now, my one and only concern...we used to use this as their actual cage flooring (the above idea is OUTSIDE their cages), but we had to take it out and turn over the pegboard floor because Flower was chewing up her linoleum and we didn't want her to get a GI blockage from it.
So, maybe try something they CAN be okay in nibbling, like plywood...and then put the linoleum underneath (so it can't just soak through the pegboard) and have the linoleum just smaller than the plywood so they can't get to it?
Anyway, those are my thoughts...because my unspayed girls do tend to "mark" outside each other's cages when they're out.
Now, if you find that this started with the arrival of the new bun, you can try the above anyway...and in that instance, it sounds like it's just everyone making SURE the new bun knows they were there first, and that their scent is still around. They'll more than likely stop if this is the case (but it'd probably be around a few weeks/a month before they stopped).
So, there ya have it...my idea.
Hugs to ya'll!
Rosie*